[PATCH v2 0/2] drm: Support framebuffer panning

[PATCH v2 0/2] drm: Support framebuffer panning

[Maxime Ripard]

Hi,

This is a respin of the previous serie called "Support fast framebuffer
panning for i.MX6" made by Stefan 6 monthes ago. The imx6 bits have been
removed, and the comments that were made at that time fixed (hopefully).

Let me know what you think,
Maxime

Changes from v1:
  - Added drm_fb_helper_ioctl to DRM_FB_HELPER_DEFAULT_OPS
  - Expanded a bit the kerneldoc for drm_fb_helper_ioctl
  - Added some locking to drm_fb_helper_ioctl
  - Checked that the framebuffer is indeed attached before allowing ioctl
  - Added a module parameter to specify the number of framebuffers to
    allocate

Initial cover letter: Support fast framebuffer panning for i.MX6

im currently working on supporting double/tripple buffering for the
framebuffer emulation on the i.MX6.  While working on it I noticed that the
mainline kernel does not support some features in the generic drm
framebuffer emulation for framebuffer panning and vsync synchronisation.
They are needed for simple framebuffer applications and some OpenGL
libraries using double buffering with FBIOPUT_VSCREENINFO,
FBIO_WAITFORVSYNC and FBIOPAN_DISPLAY.

Stefan Christ (1):
  drm/fb_helper: implement ioctl FBIO_WAITFORVSYNC

Xinliang Liu (1):
  drm/cma-helper: Add multi buffer support for cma fbdev

 drivers/gpu/drm/Kconfig             |  8 ++++-
 drivers/gpu/drm/drm_fb_cma_helper.c |  8 +++-
 drivers/gpu/drm/drm_fb_helper.c     | 55 ++++++++++++++++++++++++++++++-
 include/drm/drm_fb_helper.h         |  5 ++-
 4 files changed, 74 insertions(+), 2 deletions(-)

base-commit: 8b394ae674998d4ade6cb48aec3fca5445908dfe
-- 
git-series 0.8.11

[PATCH v2 0/2] drm: Support framebuffer panning

[Maxime Ripard]

Hi,

This is a respin of the previous serie called "Support fast framebuffer
panning for i.MX6" made by Stefan 6 monthes ago. The imx6 bits have been
removed, and the comments that were made at that time fixed (hopefully).

Let me know what you think,
Maxime

Changes from v1:
  - Added drm_fb_helper_ioctl to DRM_FB_HELPER_DEFAULT_OPS
  - Expanded a bit the kerneldoc for drm_fb_helper_ioctl
  - Added some locking to drm_fb_helper_ioctl
  - Checked that the framebuffer is indeed attached before allowing ioctl
  - Added a module parameter to specify the number of framebuffers to
    allocate

Initial cover letter: Support fast framebuffer panning for i.MX6

im currently working on supporting double/tripple buffering for the
framebuffer emulation on the i.MX6.  While working on it I noticed that the
mainline kernel does not support some features in the generic drm
framebuffer emulation for framebuffer panning and vsync synchronisation.
They are needed for simple framebuffer applications and some OpenGL
libraries using double buffering with FBIOPUT_VSCREENINFO,
FBIO_WAITFORVSYNC and FBIOPAN_DISPLAY.

Stefan Christ (1):
  drm/fb_helper: implement ioctl FBIO_WAITFORVSYNC

Xinliang Liu (1):
  drm/cma-helper: Add multi buffer support for cma fbdev

 drivers/gpu/drm/Kconfig             |  8 ++++-
 drivers/gpu/drm/drm_fb_cma_helper.c |  8 +++-
 drivers/gpu/drm/drm_fb_helper.c     | 55 ++++++++++++++++++++++++++++++-
 include/drm/drm_fb_helper.h         |  5 ++-
 4 files changed, 74 insertions(+), 2 deletions(-)

base-commit: 8b394ae674998d4ade6cb48aec3fca5445908dfe
-- 
git-series 0.8.11
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

[PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Maxime Ripard]

From: Xinliang Liu <xinliang.liu@linaro.org>

This patch add a config to support to create multi buffer for cma fbdev.
Such as double buffer and triple buffer.

Cma fbdev is convient to add a legency fbdev. And still many Android
devices use fbdev now and at least double buffer is needed for these
Android devices, so that a buffer flip can be operated. It will need
some time for Android device vendors to abondon legency fbdev. So multi
buffer for fbdev is needed.

Signed-off-by: Xinliang Liu <xinliang.liu@linaro.org>
[s.christ@phytec.de: Picking patch from
                     https://lkml.org/lkml/2015/9/14/188]
Signed-off-by: Stefan Christ <s.christ@phytec.de>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
---
 drivers/gpu/drm/Kconfig             | 8 ++++++++
 drivers/gpu/drm/drm_fb_cma_helper.c | 8 +++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index ebfe8404c25f..2ca9bb26a4e4 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -121,6 +121,14 @@ config DRM_KMS_CMA_HELPER
 	help
 	  Choose this if you need the KMS CMA helper functions
 
+config DRM_CMA_FBDEV_BUFFER_NUM
+	int "Cma Fbdev Buffer Number"
+	depends on DRM_KMS_CMA_HELPER
+	default 1
+	help
+	  Defines the buffer number of cma fbdev.  Default is one buffer.
+	  For double buffer please set to 2 and 3 for triple buffer.
+
 source "drivers/gpu/drm/i2c/Kconfig"
 
 source "drivers/gpu/drm/arm/Kconfig"
diff --git a/drivers/gpu/drm/drm_fb_cma_helper.c b/drivers/gpu/drm/drm_fb_cma_helper.c
index 81b3558302b5..e3f8b9e720a0 100644
--- a/drivers/gpu/drm/drm_fb_cma_helper.c
+++ b/drivers/gpu/drm/drm_fb_cma_helper.c
@@ -411,6 +411,12 @@ static void drm_fbdev_cma_defio_fini(struct fb_info *fbi)
 	kfree(fbi->fbops);
 }
 
+static int fbdev_num_buffers = CONFIG_DRM_CMA_FBDEV_BUFFER_NUM;
+module_param(fbdev_num_buffers, int, 0444);
+MODULE_PARM_DESC(fbdev_num_buffers,
+		 "Number of frame buffers to allocate [default="
+		 __MODULE_STRING(CONFIG_DRM_CMA_FBDEV_BUFFER_NUM) "]");
+
 /*
  * For use in a (struct drm_fb_helper_funcs *)->fb_probe callback function that
  * needs custom struct drm_framebuffer_funcs, like dirty() for deferred_io use.
@@ -437,7 +443,7 @@ int drm_fbdev_cma_create_with_funcs(struct drm_fb_helper *helper,
 	bytes_per_pixel = DIV_ROUND_UP(sizes->surface_bpp, 8);
 
 	mode_cmd.width = sizes->surface_width;
-	mode_cmd.height = sizes->surface_height;
+	mode_cmd.height = sizes->surface_height * fbdev_num_buffers;
 	mode_cmd.pitches[0] = sizes->surface_width * bytes_per_pixel;
 	mode_cmd.pixel_format = drm_mode_legacy_fb_format(sizes->surface_bpp,
 		sizes->surface_depth);
-- 
git-series 0.8.11

[PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Maxime Ripard]

From: Xinliang Liu <xinliang.liu@linaro.org>

This patch add a config to support to create multi buffer for cma fbdev.
Such as double buffer and triple buffer.

Cma fbdev is convient to add a legency fbdev. And still many Android
devices use fbdev now and at least double buffer is needed for these
Android devices, so that a buffer flip can be operated. It will need
some time for Android device vendors to abondon legency fbdev. So multi
buffer for fbdev is needed.

Signed-off-by: Xinliang Liu <xinliang.liu@linaro.org>
[s.christ@phytec.de: Picking patch from
                     https://lkml.org/lkml/2015/9/14/188]
Signed-off-by: Stefan Christ <s.christ@phytec.de>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
---
 drivers/gpu/drm/Kconfig             | 8 ++++++++
 drivers/gpu/drm/drm_fb_cma_helper.c | 8 +++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index ebfe8404c25f..2ca9bb26a4e4 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -121,6 +121,14 @@ config DRM_KMS_CMA_HELPER
 	help
 	  Choose this if you need the KMS CMA helper functions
 
+config DRM_CMA_FBDEV_BUFFER_NUM
+	int "Cma Fbdev Buffer Number"
+	depends on DRM_KMS_CMA_HELPER
+	default 1
+	help
+	  Defines the buffer number of cma fbdev.  Default is one buffer.
+	  For double buffer please set to 2 and 3 for triple buffer.
+
 source "drivers/gpu/drm/i2c/Kconfig"
 
 source "drivers/gpu/drm/arm/Kconfig"
diff --git a/drivers/gpu/drm/drm_fb_cma_helper.c b/drivers/gpu/drm/drm_fb_cma_helper.c
index 81b3558302b5..e3f8b9e720a0 100644
--- a/drivers/gpu/drm/drm_fb_cma_helper.c
+++ b/drivers/gpu/drm/drm_fb_cma_helper.c
@@ -411,6 +411,12 @@ static void drm_fbdev_cma_defio_fini(struct fb_info *fbi)
 	kfree(fbi->fbops);
 }
 
+static int fbdev_num_buffers = CONFIG_DRM_CMA_FBDEV_BUFFER_NUM;
+module_param(fbdev_num_buffers, int, 0444);
+MODULE_PARM_DESC(fbdev_num_buffers,
+		 "Number of frame buffers to allocate [default="
+		 __MODULE_STRING(CONFIG_DRM_CMA_FBDEV_BUFFER_NUM) "]");
+
 /*
  * For use in a (struct drm_fb_helper_funcs *)->fb_probe callback function that
  * needs custom struct drm_framebuffer_funcs, like dirty() for deferred_io use.
@@ -437,7 +443,7 @@ int drm_fbdev_cma_create_with_funcs(struct drm_fb_helper *helper,
 	bytes_per_pixel = DIV_ROUND_UP(sizes->surface_bpp, 8);
 
 	mode_cmd.width = sizes->surface_width;
-	mode_cmd.height = sizes->surface_height;
+	mode_cmd.height = sizes->surface_height * fbdev_num_buffers;
 	mode_cmd.pitches[0] = sizes->surface_width * bytes_per_pixel;
 	mode_cmd.pixel_format = drm_mode_legacy_fb_format(sizes->surface_bpp,
 		sizes->surface_depth);
-- 
git-series 0.8.11
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

Re: [PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Daniel Vetter]

On Thu, Feb 02, 2017 at 11:31:56AM +0100, Maxime Ripard wrote:
> From: Xinliang Liu <xinliang.liu@linaro.org>
> 
> This patch add a config to support to create multi buffer for cma fbdev.
> Such as double buffer and triple buffer.
> 
> Cma fbdev is convient to add a legency fbdev. And still many Android
> devices use fbdev now and at least double buffer is needed for these
> Android devices, so that a buffer flip can be operated. It will need
> some time for Android device vendors to abondon legency fbdev. So multi
> buffer for fbdev is needed.
> 
> Signed-off-by: Xinliang Liu <xinliang.liu@linaro.org>
> [s.christ@phytec.de: Picking patch from
>                      https://lkml.org/lkml/2015/9/14/188]
> Signed-off-by: Stefan Christ <s.christ@phytec.de>
> Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> ---
>  drivers/gpu/drm/Kconfig             | 8 ++++++++
>  drivers/gpu/drm/drm_fb_cma_helper.c | 8 +++++++-
>  2 files changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index ebfe8404c25f..2ca9bb26a4e4 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -121,6 +121,14 @@ config DRM_KMS_CMA_HELPER
>  	help
>  	  Choose this if you need the KMS CMA helper functions
>  
> +config DRM_CMA_FBDEV_BUFFER_NUM
> +	int "Cma Fbdev Buffer Number"
> +	depends on DRM_KMS_CMA_HELPER
> +	default 1
> +	help
> +	  Defines the buffer number of cma fbdev.  Default is one buffer.
> +	  For double buffer please set to 2 and 3 for triple buffer.
> +
>  source "drivers/gpu/drm/i2c/Kconfig"
>  
>  source "drivers/gpu/drm/arm/Kconfig"
> diff --git a/drivers/gpu/drm/drm_fb_cma_helper.c b/drivers/gpu/drm/drm_fb_cma_helper.c
> index 81b3558302b5..e3f8b9e720a0 100644
> --- a/drivers/gpu/drm/drm_fb_cma_helper.c
> +++ b/drivers/gpu/drm/drm_fb_cma_helper.c
> @@ -411,6 +411,12 @@ static void drm_fbdev_cma_defio_fini(struct fb_info *fbi)
>  	kfree(fbi->fbops);
>  }
>  
> +static int fbdev_num_buffers = CONFIG_DRM_CMA_FBDEV_BUFFER_NUM;
> +module_param(fbdev_num_buffers, int, 0444);
> +MODULE_PARM_DESC(fbdev_num_buffers,
> +		 "Number of frame buffers to allocate [default="
> +		 __MODULE_STRING(CONFIG_DRM_CMA_FBDEV_BUFFER_NUM) "]");

Pure bikshed: Should this be an overallocation %? 200 for
double-buffering, 100 as the default?

Slightly less bikesheddy: Can't we do this in the core helpers somehow?
I'd be nice if this is not cma specific. If it's not possible, I'd at
least move the symbol to drm_fb_helper.c, and add some kernel-doc around
it. That allows any other non-cma driver to at least implement support for
this. That also has the benefit of featuring it more prominently, in our
docs.

Besides these bikesheds/question, looks all reasonable to me. If you can
get some more acks would be great, but will merge anyway.
-Daniel

> +
>  /*
>   * For use in a (struct drm_fb_helper_funcs *)->fb_probe callback function that
>   * needs custom struct drm_framebuffer_funcs, like dirty() for deferred_io use.
> @@ -437,7 +443,7 @@ int drm_fbdev_cma_create_with_funcs(struct drm_fb_helper *helper,
>  	bytes_per_pixel = DIV_ROUND_UP(sizes->surface_bpp, 8);
>  
>  	mode_cmd.width = sizes->surface_width;
> -	mode_cmd.height = sizes->surface_height;
> +	mode_cmd.height = sizes->surface_height * fbdev_num_buffers;
>  	mode_cmd.pitches[0] = sizes->surface_width * bytes_per_pixel;
>  	mode_cmd.pixel_format = drm_mode_legacy_fb_format(sizes->surface_bpp,
>  		sizes->surface_depth);
> -- 
> git-series 0.8.11
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

Re: [PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Daniel Vetter]

On Thu, Feb 02, 2017 at 11:31:56AM +0100, Maxime Ripard wrote:
> From: Xinliang Liu <xinliang.liu@linaro.org>
> 
> This patch add a config to support to create multi buffer for cma fbdev.
> Such as double buffer and triple buffer.
> 
> Cma fbdev is convient to add a legency fbdev. And still many Android
> devices use fbdev now and at least double buffer is needed for these
> Android devices, so that a buffer flip can be operated. It will need
> some time for Android device vendors to abondon legency fbdev. So multi
> buffer for fbdev is needed.
> 
> Signed-off-by: Xinliang Liu <xinliang.liu@linaro.org>
> [s.christ@phytec.de: Picking patch from
>                      https://lkml.org/lkml/2015/9/14/188]
> Signed-off-by: Stefan Christ <s.christ@phytec.de>
> Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> ---
>  drivers/gpu/drm/Kconfig             | 8 ++++++++
>  drivers/gpu/drm/drm_fb_cma_helper.c | 8 +++++++-
>  2 files changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index ebfe8404c25f..2ca9bb26a4e4 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -121,6 +121,14 @@ config DRM_KMS_CMA_HELPER
>  	help
>  	  Choose this if you need the KMS CMA helper functions
>  
> +config DRM_CMA_FBDEV_BUFFER_NUM
> +	int "Cma Fbdev Buffer Number"
> +	depends on DRM_KMS_CMA_HELPER
> +	default 1
> +	help
> +	  Defines the buffer number of cma fbdev.  Default is one buffer.
> +	  For double buffer please set to 2 and 3 for triple buffer.
> +
>  source "drivers/gpu/drm/i2c/Kconfig"
>  
>  source "drivers/gpu/drm/arm/Kconfig"
> diff --git a/drivers/gpu/drm/drm_fb_cma_helper.c b/drivers/gpu/drm/drm_fb_cma_helper.c
> index 81b3558302b5..e3f8b9e720a0 100644
> --- a/drivers/gpu/drm/drm_fb_cma_helper.c
> +++ b/drivers/gpu/drm/drm_fb_cma_helper.c
> @@ -411,6 +411,12 @@ static void drm_fbdev_cma_defio_fini(struct fb_info *fbi)
>  	kfree(fbi->fbops);
>  }
>  
> +static int fbdev_num_buffers = CONFIG_DRM_CMA_FBDEV_BUFFER_NUM;
> +module_param(fbdev_num_buffers, int, 0444);
> +MODULE_PARM_DESC(fbdev_num_buffers,
> +		 "Number of frame buffers to allocate [default="
> +		 __MODULE_STRING(CONFIG_DRM_CMA_FBDEV_BUFFER_NUM) "]");

Pure bikshed: Should this be an overallocation %? 200 for
double-buffering, 100 as the default?

Slightly less bikesheddy: Can't we do this in the core helpers somehow?
I'd be nice if this is not cma specific. If it's not possible, I'd at
least move the symbol to drm_fb_helper.c, and add some kernel-doc around
it. That allows any other non-cma driver to at least implement support for
this. That also has the benefit of featuring it more prominently, in our
docs.

Besides these bikesheds/question, looks all reasonable to me. If you can
get some more acks would be great, but will merge anyway.
-Daniel

> +
>  /*
>   * For use in a (struct drm_fb_helper_funcs *)->fb_probe callback function that
>   * needs custom struct drm_framebuffer_funcs, like dirty() for deferred_io use.
> @@ -437,7 +443,7 @@ int drm_fbdev_cma_create_with_funcs(struct drm_fb_helper *helper,
>  	bytes_per_pixel = DIV_ROUND_UP(sizes->surface_bpp, 8);
>  
>  	mode_cmd.width = sizes->surface_width;
> -	mode_cmd.height = sizes->surface_height;
> +	mode_cmd.height = sizes->surface_height * fbdev_num_buffers;
>  	mode_cmd.pitches[0] = sizes->surface_width * bytes_per_pixel;
>  	mode_cmd.pixel_format = drm_mode_legacy_fb_format(sizes->surface_bpp,
>  		sizes->surface_depth);
> -- 
> git-series 0.8.11
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

Re: [PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Maxime Ripard]

[-- Attachment #1: Type: text/plain, Size: 3314 bytes --]

Hi Daniel,

On Thu, Feb 09, 2017 at 06:04:38PM +0100, Daniel Vetter wrote:
> On Thu, Feb 02, 2017 at 11:31:56AM +0100, Maxime Ripard wrote:
> > From: Xinliang Liu <xinliang.liu@linaro.org>
> > 
> > This patch add a config to support to create multi buffer for cma fbdev.
> > Such as double buffer and triple buffer.
> > 
> > Cma fbdev is convient to add a legency fbdev. And still many Android
> > devices use fbdev now and at least double buffer is needed for these
> > Android devices, so that a buffer flip can be operated. It will need
> > some time for Android device vendors to abondon legency fbdev. So multi
> > buffer for fbdev is needed.
> > 
> > Signed-off-by: Xinliang Liu <xinliang.liu@linaro.org>
> > [s.christ@phytec.de: Picking patch from
> >                      https://lkml.org/lkml/2015/9/14/188]
> > Signed-off-by: Stefan Christ <s.christ@phytec.de>
> > Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> > ---
> >  drivers/gpu/drm/Kconfig             | 8 ++++++++
> >  drivers/gpu/drm/drm_fb_cma_helper.c | 8 +++++++-
> >  2 files changed, 15 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> > index ebfe8404c25f..2ca9bb26a4e4 100644
> > --- a/drivers/gpu/drm/Kconfig
> > +++ b/drivers/gpu/drm/Kconfig
> > @@ -121,6 +121,14 @@ config DRM_KMS_CMA_HELPER
> >  	help
> >  	  Choose this if you need the KMS CMA helper functions
> >  
> > +config DRM_CMA_FBDEV_BUFFER_NUM
> > +	int "Cma Fbdev Buffer Number"
> > +	depends on DRM_KMS_CMA_HELPER
> > +	default 1
> > +	help
> > +	  Defines the buffer number of cma fbdev.  Default is one buffer.
> > +	  For double buffer please set to 2 and 3 for triple buffer.
> > +
> >  source "drivers/gpu/drm/i2c/Kconfig"
> >  
> >  source "drivers/gpu/drm/arm/Kconfig"
> > diff --git a/drivers/gpu/drm/drm_fb_cma_helper.c b/drivers/gpu/drm/drm_fb_cma_helper.c
> > index 81b3558302b5..e3f8b9e720a0 100644
> > --- a/drivers/gpu/drm/drm_fb_cma_helper.c
> > +++ b/drivers/gpu/drm/drm_fb_cma_helper.c
> > @@ -411,6 +411,12 @@ static void drm_fbdev_cma_defio_fini(struct fb_info *fbi)
> >  	kfree(fbi->fbops);
> >  }
> >  
> > +static int fbdev_num_buffers = CONFIG_DRM_CMA_FBDEV_BUFFER_NUM;
> > +module_param(fbdev_num_buffers, int, 0444);
> > +MODULE_PARM_DESC(fbdev_num_buffers,
> > +		 "Number of frame buffers to allocate [default="
> > +		 __MODULE_STRING(CONFIG_DRM_CMA_FBDEV_BUFFER_NUM) "]");
> 
> Pure bikshed: Should this be an overallocation %? 200 for
> double-buffering, 100 as the default?

I'm not against it, but would it make sense to allocate something like
120% of a buffer?

> Slightly less bikesheddy: Can't we do this in the core helpers somehow?

I guess that would move it to drm_fb_helper_single_fb_probe then? It
makes sense.

> I'd be nice if this is not cma specific. If it's not possible, I'd at
> least move the symbol to drm_fb_helper.c, and add some kernel-doc around
> it. That allows any other non-cma driver to at least implement support for
> this. That also has the benefit of featuring it more prominently, in our
> docs.

I'll move it and add the kerneldoc.

Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

[-- Attachment #2: signature.asc --]
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Re: [PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Maxime Ripard]

[-- Attachment #1.1: Type: text/plain, Size: 3314 bytes --]

Hi Daniel,

On Thu, Feb 09, 2017 at 06:04:38PM +0100, Daniel Vetter wrote:
> On Thu, Feb 02, 2017 at 11:31:56AM +0100, Maxime Ripard wrote:
> > From: Xinliang Liu <xinliang.liu@linaro.org>
> > 
> > This patch add a config to support to create multi buffer for cma fbdev.
> > Such as double buffer and triple buffer.
> > 
> > Cma fbdev is convient to add a legency fbdev. And still many Android
> > devices use fbdev now and at least double buffer is needed for these
> > Android devices, so that a buffer flip can be operated. It will need
> > some time for Android device vendors to abondon legency fbdev. So multi
> > buffer for fbdev is needed.
> > 
> > Signed-off-by: Xinliang Liu <xinliang.liu@linaro.org>
> > [s.christ@phytec.de: Picking patch from
> >                      https://lkml.org/lkml/2015/9/14/188]
> > Signed-off-by: Stefan Christ <s.christ@phytec.de>
> > Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> > ---
> >  drivers/gpu/drm/Kconfig             | 8 ++++++++
> >  drivers/gpu/drm/drm_fb_cma_helper.c | 8 +++++++-
> >  2 files changed, 15 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> > index ebfe8404c25f..2ca9bb26a4e4 100644
> > --- a/drivers/gpu/drm/Kconfig
> > +++ b/drivers/gpu/drm/Kconfig
> > @@ -121,6 +121,14 @@ config DRM_KMS_CMA_HELPER
> >  	help
> >  	  Choose this if you need the KMS CMA helper functions
> >  
> > +config DRM_CMA_FBDEV_BUFFER_NUM
> > +	int "Cma Fbdev Buffer Number"
> > +	depends on DRM_KMS_CMA_HELPER
> > +	default 1
> > +	help
> > +	  Defines the buffer number of cma fbdev.  Default is one buffer.
> > +	  For double buffer please set to 2 and 3 for triple buffer.
> > +
> >  source "drivers/gpu/drm/i2c/Kconfig"
> >  
> >  source "drivers/gpu/drm/arm/Kconfig"
> > diff --git a/drivers/gpu/drm/drm_fb_cma_helper.c b/drivers/gpu/drm/drm_fb_cma_helper.c
> > index 81b3558302b5..e3f8b9e720a0 100644
> > --- a/drivers/gpu/drm/drm_fb_cma_helper.c
> > +++ b/drivers/gpu/drm/drm_fb_cma_helper.c
> > @@ -411,6 +411,12 @@ static void drm_fbdev_cma_defio_fini(struct fb_info *fbi)
> >  	kfree(fbi->fbops);
> >  }
> >  
> > +static int fbdev_num_buffers = CONFIG_DRM_CMA_FBDEV_BUFFER_NUM;
> > +module_param(fbdev_num_buffers, int, 0444);
> > +MODULE_PARM_DESC(fbdev_num_buffers,
> > +		 "Number of frame buffers to allocate [default="
> > +		 __MODULE_STRING(CONFIG_DRM_CMA_FBDEV_BUFFER_NUM) "]");
> 
> Pure bikshed: Should this be an overallocation %? 200 for
> double-buffering, 100 as the default?

I'm not against it, but would it make sense to allocate something like
120% of a buffer?

> Slightly less bikesheddy: Can't we do this in the core helpers somehow?

I guess that would move it to drm_fb_helper_single_fb_probe then? It
makes sense.

> I'd be nice if this is not cma specific. If it's not possible, I'd at
> least move the symbol to drm_fb_helper.c, and add some kernel-doc around
> it. That allows any other non-cma driver to at least implement support for
> this. That also has the benefit of featuring it more prominently, in our
> docs.

I'll move it and add the kerneldoc.

Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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Re: [PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Laurent Pinchart]

Hi Maxime,

Thank you for the patch.

On Thursday 02 Feb 2017 11:31:56 Maxime Ripard wrote:
> From: Xinliang Liu <xinliang.liu@linaro.org>
> 
> This patch add a config to support to create multi buffer for cma fbdev.
> Such as double buffer and triple buffer.
> 
> Cma fbdev is convient to add a legency fbdev. And still many Android
> devices use fbdev now and at least double buffer is needed for these
> Android devices, so that a buffer flip can be operated. It will need
> some time for Android device vendors to abondon legency fbdev. So multi
> buffer for fbdev is needed.

How exactly do we expect Android to move away from fbdev if we add features to 
the fbdev compat layer ? I'd much rather make it clear to them that fbdev is a 
thing from the past and that they'd better migrate now.

> Signed-off-by: Xinliang Liu <xinliang.liu@linaro.org>
> [s.christ@phytec.de: Picking patch from
>                      https://lkml.org/lkml/2015/9/14/188]
> Signed-off-by: Stefan Christ <s.christ@phytec.de>
> Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> ---
>  drivers/gpu/drm/Kconfig             | 8 ++++++++
>  drivers/gpu/drm/drm_fb_cma_helper.c | 8 +++++++-
>  2 files changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index ebfe8404c25f..2ca9bb26a4e4 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -121,6 +121,14 @@ config DRM_KMS_CMA_HELPER
>  	help
>  	  Choose this if you need the KMS CMA helper functions
> 
> +config DRM_CMA_FBDEV_BUFFER_NUM
> +	int "Cma Fbdev Buffer Number"
> +	depends on DRM_KMS_CMA_HELPER
> +	default 1
> +	help
> +	  Defines the buffer number of cma fbdev.  Default is one buffer.
> +	  For double buffer please set to 2 and 3 for triple buffer.
> +
>  source "drivers/gpu/drm/i2c/Kconfig"
> 
>  source "drivers/gpu/drm/arm/Kconfig"
> diff --git a/drivers/gpu/drm/drm_fb_cma_helper.c
> b/drivers/gpu/drm/drm_fb_cma_helper.c index 81b3558302b5..e3f8b9e720a0
> 100644
> --- a/drivers/gpu/drm/drm_fb_cma_helper.c
> +++ b/drivers/gpu/drm/drm_fb_cma_helper.c
> @@ -411,6 +411,12 @@ static void drm_fbdev_cma_defio_fini(struct fb_info
> *fbi) kfree(fbi->fbops);
>  }
> 
> +static int fbdev_num_buffers = CONFIG_DRM_CMA_FBDEV_BUFFER_NUM;
> +module_param(fbdev_num_buffers, int, 0444);
> +MODULE_PARM_DESC(fbdev_num_buffers,
> +		 "Number of frame buffers to allocate [default="
> +		 __MODULE_STRING(CONFIG_DRM_CMA_FBDEV_BUFFER_NUM) "]");
> +
>  /*
>   * For use in a (struct drm_fb_helper_funcs *)->fb_probe callback function
> that * needs custom struct drm_framebuffer_funcs, like dirty() for
> deferred_io use. @@ -437,7 +443,7 @@ int
> drm_fbdev_cma_create_with_funcs(struct drm_fb_helper *helper,
> bytes_per_pixel = DIV_ROUND_UP(sizes->surface_bpp, 8);
> 
>  	mode_cmd.width = sizes->surface_width;
> -	mode_cmd.height = sizes->surface_height;
> +	mode_cmd.height = sizes->surface_height * fbdev_num_buffers;
>  	mode_cmd.pitches[0] = sizes->surface_width * bytes_per_pixel;
>  	mode_cmd.pixel_format = drm_mode_legacy_fb_format(sizes->surface_bpp,
>  		sizes->surface_depth);

-- 
Regards,

Laurent Pinchart

Re: [PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Laurent Pinchart]

Hi Maxime,

Thank you for the patch.

On Thursday 02 Feb 2017 11:31:56 Maxime Ripard wrote:
> From: Xinliang Liu <xinliang.liu@linaro.org>
> 
> This patch add a config to support to create multi buffer for cma fbdev.
> Such as double buffer and triple buffer.
> 
> Cma fbdev is convient to add a legency fbdev. And still many Android
> devices use fbdev now and at least double buffer is needed for these
> Android devices, so that a buffer flip can be operated. It will need
> some time for Android device vendors to abondon legency fbdev. So multi
> buffer for fbdev is needed.

How exactly do we expect Android to move away from fbdev if we add features to 
the fbdev compat layer ? I'd much rather make it clear to them that fbdev is a 
thing from the past and that they'd better migrate now.

> Signed-off-by: Xinliang Liu <xinliang.liu@linaro.org>
> [s.christ@phytec.de: Picking patch from
>                      https://lkml.org/lkml/2015/9/14/188]
> Signed-off-by: Stefan Christ <s.christ@phytec.de>
> Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> ---
>  drivers/gpu/drm/Kconfig             | 8 ++++++++
>  drivers/gpu/drm/drm_fb_cma_helper.c | 8 +++++++-
>  2 files changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index ebfe8404c25f..2ca9bb26a4e4 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -121,6 +121,14 @@ config DRM_KMS_CMA_HELPER
>  	help
>  	  Choose this if you need the KMS CMA helper functions
> 
> +config DRM_CMA_FBDEV_BUFFER_NUM
> +	int "Cma Fbdev Buffer Number"
> +	depends on DRM_KMS_CMA_HELPER
> +	default 1
> +	help
> +	  Defines the buffer number of cma fbdev.  Default is one buffer.
> +	  For double buffer please set to 2 and 3 for triple buffer.
> +
>  source "drivers/gpu/drm/i2c/Kconfig"
> 
>  source "drivers/gpu/drm/arm/Kconfig"
> diff --git a/drivers/gpu/drm/drm_fb_cma_helper.c
> b/drivers/gpu/drm/drm_fb_cma_helper.c index 81b3558302b5..e3f8b9e720a0
> 100644
> --- a/drivers/gpu/drm/drm_fb_cma_helper.c
> +++ b/drivers/gpu/drm/drm_fb_cma_helper.c
> @@ -411,6 +411,12 @@ static void drm_fbdev_cma_defio_fini(struct fb_info
> *fbi) kfree(fbi->fbops);
>  }
> 
> +static int fbdev_num_buffers = CONFIG_DRM_CMA_FBDEV_BUFFER_NUM;
> +module_param(fbdev_num_buffers, int, 0444);
> +MODULE_PARM_DESC(fbdev_num_buffers,
> +		 "Number of frame buffers to allocate [default="
> +		 __MODULE_STRING(CONFIG_DRM_CMA_FBDEV_BUFFER_NUM) "]");
> +
>  /*
>   * For use in a (struct drm_fb_helper_funcs *)->fb_probe callback function
> that * needs custom struct drm_framebuffer_funcs, like dirty() for
> deferred_io use. @@ -437,7 +443,7 @@ int
> drm_fbdev_cma_create_with_funcs(struct drm_fb_helper *helper,
> bytes_per_pixel = DIV_ROUND_UP(sizes->surface_bpp, 8);
> 
>  	mode_cmd.width = sizes->surface_width;
> -	mode_cmd.height = sizes->surface_height;
> +	mode_cmd.height = sizes->surface_height * fbdev_num_buffers;
>  	mode_cmd.pitches[0] = sizes->surface_width * bytes_per_pixel;
>  	mode_cmd.pixel_format = drm_mode_legacy_fb_format(sizes->surface_bpp,
>  		sizes->surface_depth);

-- 
Regards,

Laurent Pinchart

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Re: [PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Maxime Ripard]

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Hi Laurent,

On Sun, Feb 12, 2017 at 02:28:11PM +0200, Laurent Pinchart wrote:
> Hi Maxime,
> 
> Thank you for the patch.
> 
> On Thursday 02 Feb 2017 11:31:56 Maxime Ripard wrote:
> > From: Xinliang Liu <xinliang.liu@linaro.org>
> > 
> > This patch add a config to support to create multi buffer for cma fbdev.
> > Such as double buffer and triple buffer.
> > 
> > Cma fbdev is convient to add a legency fbdev. And still many Android
> > devices use fbdev now and at least double buffer is needed for these
> > Android devices, so that a buffer flip can be operated. It will need
> > some time for Android device vendors to abondon legency fbdev. So multi
> > buffer for fbdev is needed.
> 
> How exactly do we expect Android to move away from fbdev if we add features to 
> the fbdev compat layer ? I'd much rather make it clear to them that fbdev is a 
> thing from the past and that they'd better migrate now.

If your point is that merging this patch will slow down the Android
move away from fbdev, I disagree with that (obviously).

I don't care at all about Android on my platform of choice, but don't
see how that merging this patch will change anything.

Let's be honest, Android trees typically have thousands of patches on
top of mainline. Do you think a simple, 15 LoC, patch will make any
difference to vendors? If they want to stay on fbdev and have that
feature, they'll just merge this patch, done.

However, what I do see is that three different people/organisations
have now expressed interest in that feature, on three different
SoCs. If that patch needed a significant rework of the fbdev layer,
then yes, I might agree that it's not worth it. But in this case, it's
pretty trivial.

The only people you're "punishing" here with that kind of concern are
the people who actually play fair and want not to have any patches and
everything upstream.

I guess a much better strategy would be to provide an incentive to
moving to KMS. And I truely think there's one already, so it's just a
matter of time before people switch over. Fbdev emulation or not.

Ma

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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Re: [PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Maxime Ripard]

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Hi Laurent,

On Sun, Feb 12, 2017 at 02:28:11PM +0200, Laurent Pinchart wrote:
> Hi Maxime,
> 
> Thank you for the patch.
> 
> On Thursday 02 Feb 2017 11:31:56 Maxime Ripard wrote:
> > From: Xinliang Liu <xinliang.liu@linaro.org>
> > 
> > This patch add a config to support to create multi buffer for cma fbdev.
> > Such as double buffer and triple buffer.
> > 
> > Cma fbdev is convient to add a legency fbdev. And still many Android
> > devices use fbdev now and at least double buffer is needed for these
> > Android devices, so that a buffer flip can be operated. It will need
> > some time for Android device vendors to abondon legency fbdev. So multi
> > buffer for fbdev is needed.
> 
> How exactly do we expect Android to move away from fbdev if we add features to 
> the fbdev compat layer ? I'd much rather make it clear to them that fbdev is a 
> thing from the past and that they'd better migrate now.

If your point is that merging this patch will slow down the Android
move away from fbdev, I disagree with that (obviously).

I don't care at all about Android on my platform of choice, but don't
see how that merging this patch will change anything.

Let's be honest, Android trees typically have thousands of patches on
top of mainline. Do you think a simple, 15 LoC, patch will make any
difference to vendors? If they want to stay on fbdev and have that
feature, they'll just merge this patch, done.

However, what I do see is that three different people/organisations
have now expressed interest in that feature, on three different
SoCs. If that patch needed a significant rework of the fbdev layer,
then yes, I might agree that it's not worth it. But in this case, it's
pretty trivial.

The only people you're "punishing" here with that kind of concern are
the people who actually play fair and want not to have any patches and
everything upstream.

I guess a much better strategy would be to provide an incentive to
moving to KMS. And I truely think there's one already, so it's just a
matter of time before people switch over. Fbdev emulation or not.

Ma

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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Re: [PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Daniel Stone]

Hi Maxime,

On 13 February 2017 at 10:54, Maxime Ripard
<maxime.ripard@free-electrons.com> wrote:
> On Sun, Feb 12, 2017 at 02:28:11PM +0200, Laurent Pinchart wrote:
>> On Thursday 02 Feb 2017 11:31:56 Maxime Ripard wrote:
>> > This patch add a config to support to create multi buffer for cma fbdev.
>> > Such as double buffer and triple buffer.
>> >
>> > Cma fbdev is convient to add a legency fbdev. And still many Android
>> > devices use fbdev now and at least double buffer is needed for these
>> > Android devices, so that a buffer flip can be operated. It will need
>> > some time for Android device vendors to abondon legency fbdev. So multi
>> > buffer for fbdev is needed.
>>
>> How exactly do we expect Android to move away from fbdev if we add features to
>> the fbdev compat layer ? I'd much rather make it clear to them that fbdev is a
>> thing from the past and that they'd better migrate now.
>
> If your point is that merging this patch will slow down the Android
> move away from fbdev, I disagree with that (obviously).
>
> I don't care at all about Android on my platform of choice, but don't
> see how that merging this patch will change anything.
>
> Let's be honest, Android trees typically have thousands of patches on
> top of mainline. Do you think a simple, 15 LoC, patch will make any
> difference to vendors? If they want to stay on fbdev and have that
> feature, they'll just merge this patch, done.

So, in that case, why not just let them do that? They'd already have
to add patches to use this, surely; we don't have anything in mainline
kernels which allows people to actually use this larger allocation.
Apart from software mmap() and using panning to do flips, but I'm
taking it as a given that people shipping Android on their devices
aren't using software rendering.

> However, what I do see is that three different people/organisations
> have now expressed interest in that feature, on three different
> SoCs. If that patch needed a significant rework of the fbdev layer,
> then yes, I might agree that it's not worth it. But in this case, it's
> pretty trivial.
>
> The only people you're "punishing" here with that kind of concern are
> the people who actually play fair and want not to have any patches and
> everything upstream.

I would hazard a guess that most users of this have out-of-tree GPU drivers.

> I guess a much better strategy would be to provide an incentive to
> moving to KMS. And I truely think there's one already, so it's just a
> matter of time before people switch over. Fbdev emulation or not.

The concern makes sense, but on the other hand, fbdev is deprecated:
no new drivers, and no new features.

Cheers,
Daniel

Re: [PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Daniel Stone]

Hi Maxime,

On 13 February 2017 at 10:54, Maxime Ripard
<maxime.ripard@free-electrons.com> wrote:
> On Sun, Feb 12, 2017 at 02:28:11PM +0200, Laurent Pinchart wrote:
>> On Thursday 02 Feb 2017 11:31:56 Maxime Ripard wrote:
>> > This patch add a config to support to create multi buffer for cma fbdev.
>> > Such as double buffer and triple buffer.
>> >
>> > Cma fbdev is convient to add a legency fbdev. And still many Android
>> > devices use fbdev now and at least double buffer is needed for these
>> > Android devices, so that a buffer flip can be operated. It will need
>> > some time for Android device vendors to abondon legency fbdev. So multi
>> > buffer for fbdev is needed.
>>
>> How exactly do we expect Android to move away from fbdev if we add features to
>> the fbdev compat layer ? I'd much rather make it clear to them that fbdev is a
>> thing from the past and that they'd better migrate now.
>
> If your point is that merging this patch will slow down the Android
> move away from fbdev, I disagree with that (obviously).
>
> I don't care at all about Android on my platform of choice, but don't
> see how that merging this patch will change anything.
>
> Let's be honest, Android trees typically have thousands of patches on
> top of mainline. Do you think a simple, 15 LoC, patch will make any
> difference to vendors? If they want to stay on fbdev and have that
> feature, they'll just merge this patch, done.

So, in that case, why not just let them do that? They'd already have
to add patches to use this, surely; we don't have anything in mainline
kernels which allows people to actually use this larger allocation.
Apart from software mmap() and using panning to do flips, but I'm
taking it as a given that people shipping Android on their devices
aren't using software rendering.

> However, what I do see is that three different people/organisations
> have now expressed interest in that feature, on three different
> SoCs. If that patch needed a significant rework of the fbdev layer,
> then yes, I might agree that it's not worth it. But in this case, it's
> pretty trivial.
>
> The only people you're "punishing" here with that kind of concern are
> the people who actually play fair and want not to have any patches and
> everything upstream.

I would hazard a guess that most users of this have out-of-tree GPU drivers.

> I guess a much better strategy would be to provide an incentive to
> moving to KMS. And I truely think there's one already, so it's just a
> matter of time before people switch over. Fbdev emulation or not.

The concern makes sense, but on the other hand, fbdev is deprecated:
no new drivers, and no new features.

Cheers,
Daniel
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Re: [PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Daniel Vetter]

On Mon, Feb 13, 2017 at 11:20:51AM +0000, Daniel Stone wrote:
> Hi Maxime,
> 
> On 13 February 2017 at 10:54, Maxime Ripard
> <maxime.ripard@free-electrons.com> wrote:
> > On Sun, Feb 12, 2017 at 02:28:11PM +0200, Laurent Pinchart wrote:
> >> On Thursday 02 Feb 2017 11:31:56 Maxime Ripard wrote:
> >> > This patch add a config to support to create multi buffer for cma fbdev.
> >> > Such as double buffer and triple buffer.
> >> >
> >> > Cma fbdev is convient to add a legency fbdev. And still many Android
> >> > devices use fbdev now and at least double buffer is needed for these
> >> > Android devices, so that a buffer flip can be operated. It will need
> >> > some time for Android device vendors to abondon legency fbdev. So multi
> >> > buffer for fbdev is needed.
> >>
> >> How exactly do we expect Android to move away from fbdev if we add features to
> >> the fbdev compat layer ? I'd much rather make it clear to them that fbdev is a
> >> thing from the past and that they'd better migrate now.
> >
> > If your point is that merging this patch will slow down the Android
> > move away from fbdev, I disagree with that (obviously).
> >
> > I don't care at all about Android on my platform of choice, but don't
> > see how that merging this patch will change anything.
> >
> > Let's be honest, Android trees typically have thousands of patches on
> > top of mainline. Do you think a simple, 15 LoC, patch will make any
> > difference to vendors? If they want to stay on fbdev and have that
> > feature, they'll just merge this patch, done.
> 
> So, in that case, why not just let them do that? They'd already have
> to add patches to use this, surely; we don't have anything in mainline
> kernels which allows people to actually use this larger allocation.
> Apart from software mmap() and using panning to do flips, but I'm
> taking it as a given that people shipping Android on their devices
> aren't using software rendering.

I think we need to make a distinction between fbdev the subsystem in the
kernel, and fbdev the uabi:

- fbdev the subsystem is completely dead in upstream. I think we have full
  agreement on that.
- fbdev the uabi isn't, and if we can get more users from fbdev based
  drivers to kms/atomic drivers by adding fairly simple stuff like this,
  I'm all for it.

Which means: Yes, I fully plan to merge this, it makes sense. It even
_helps_ by making fbdev-the-subsystem even deader. Making live hard for
out-of-tree folks or folks with shit userspace doesn't make sense, at
least if the only benefit for us is that we'll feel pure about our
intentions :-)

Cheers, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

Re: [PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Daniel Vetter]

On Mon, Feb 13, 2017 at 11:20:51AM +0000, Daniel Stone wrote:
> Hi Maxime,
> 
> On 13 February 2017 at 10:54, Maxime Ripard
> <maxime.ripard@free-electrons.com> wrote:
> > On Sun, Feb 12, 2017 at 02:28:11PM +0200, Laurent Pinchart wrote:
> >> On Thursday 02 Feb 2017 11:31:56 Maxime Ripard wrote:
> >> > This patch add a config to support to create multi buffer for cma fbdev.
> >> > Such as double buffer and triple buffer.
> >> >
> >> > Cma fbdev is convient to add a legency fbdev. And still many Android
> >> > devices use fbdev now and at least double buffer is needed for these
> >> > Android devices, so that a buffer flip can be operated. It will need
> >> > some time for Android device vendors to abondon legency fbdev. So multi
> >> > buffer for fbdev is needed.
> >>
> >> How exactly do we expect Android to move away from fbdev if we add features to
> >> the fbdev compat layer ? I'd much rather make it clear to them that fbdev is a
> >> thing from the past and that they'd better migrate now.
> >
> > If your point is that merging this patch will slow down the Android
> > move away from fbdev, I disagree with that (obviously).
> >
> > I don't care at all about Android on my platform of choice, but don't
> > see how that merging this patch will change anything.
> >
> > Let's be honest, Android trees typically have thousands of patches on
> > top of mainline. Do you think a simple, 15 LoC, patch will make any
> > difference to vendors? If they want to stay on fbdev and have that
> > feature, they'll just merge this patch, done.
> 
> So, in that case, why not just let them do that? They'd already have
> to add patches to use this, surely; we don't have anything in mainline
> kernels which allows people to actually use this larger allocation.
> Apart from software mmap() and using panning to do flips, but I'm
> taking it as a given that people shipping Android on their devices
> aren't using software rendering.

I think we need to make a distinction between fbdev the subsystem in the
kernel, and fbdev the uabi:

- fbdev the subsystem is completely dead in upstream. I think we have full
  agreement on that.
- fbdev the uabi isn't, and if we can get more users from fbdev based
  drivers to kms/atomic drivers by adding fairly simple stuff like this,
  I'm all for it.

Which means: Yes, I fully plan to merge this, it makes sense. It even
_helps_ by making fbdev-the-subsystem even deader. Making live hard for
out-of-tree folks or folks with shit userspace doesn't make sense, at
least if the only benefit for us is that we'll feel pure about our
intentions :-)

Cheers, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Laurent Pinchart]

Hi Daniel,

On Tuesday 14 Feb 2017 21:09:51 Daniel Vetter wrote:
> On Mon, Feb 13, 2017 at 11:20:51AM +0000, Daniel Stone wrote:
> > On 13 February 2017 at 10:54, Maxime Ripard wrote:
> >> On Sun, Feb 12, 2017 at 02:28:11PM +0200, Laurent Pinchart wrote:
> >>> On Thursday 02 Feb 2017 11:31:56 Maxime Ripard wrote:
> >>>> This patch add a config to support to create multi buffer for cma
> >>>> fbdev. Such as double buffer and triple buffer.
> >>>> 
> >>>> Cma fbdev is convient to add a legency fbdev. And still many Android
> >>>> devices use fbdev now and at least double buffer is needed for these
> >>>> Android devices, so that a buffer flip can be operated. It will need
> >>>> some time for Android device vendors to abondon legency fbdev. So
> >>>> multi buffer for fbdev is needed.
> >>> 
> >>> How exactly do we expect Android to move away from fbdev if we add
> >>> features to the fbdev compat layer ? I'd much rather make it clear to
> >>> them that fbdev is a thing from the past and that they'd better
> >>> migrate now.
> >> 
> >> If your point is that merging this patch will slow down the Android
> >> move away from fbdev, I disagree with that (obviously).
> >> 
> >> I don't care at all about Android on my platform of choice, but don't
> >> see how that merging this patch will change anything.
> >> 
> >> Let's be honest, Android trees typically have thousands of patches on
> >> top of mainline. Do you think a simple, 15 LoC, patch will make any
> >> difference to vendors? If they want to stay on fbdev and have that
> >> feature, they'll just merge this patch, done.
> > 
> > So, in that case, why not just let them do that? They'd already have
> > to add patches to use this, surely; we don't have anything in mainline
> > kernels which allows people to actually use this larger allocation.
> > Apart from software mmap() and using panning to do flips, but I'm
> > taking it as a given that people shipping Android on their devices
> > aren't using software rendering.
> 
> I think we need to make a distinction between fbdev the subsystem in the
> kernel, and fbdev the uabi:
> 
> - fbdev the subsystem is completely dead in upstream. I think we have full
>   agreement on that.
> - fbdev the uabi isn't, and if we can get more users from fbdev based
>   drivers to kms/atomic drivers by adding fairly simple stuff like this,
>   I'm all for it.

The real question, in my opinion, is how to get more users for the DRM/KMS 
userspace API, to help killing the fbdev API. What's the incentive for 
userspace to migrate if we tell them that we're going to support the fbdev API 
forever, and will even go through the trouble of extending the supported 
feature set ? I have a customer who wouldn't have migrated their userspace to 
DRM/KMS if these two patches had been merged a few years ago. I'd rather 
*reduce* the supported feature set over time until we can finally switch fbdev 
off.

> Which means: Yes, I fully plan to merge this, it makes sense. It even
> _helps_ by making fbdev-the-subsystem even deader. Making live hard for
> out-of-tree folks or folks with shit userspace doesn't make sense, at
> least if the only benefit for us is that we'll feel pure about our
> intentions :-)

-- 
Regards,

Laurent Pinchart

Re: [PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Laurent Pinchart]

Hi Daniel,

On Tuesday 14 Feb 2017 21:09:51 Daniel Vetter wrote:
> On Mon, Feb 13, 2017 at 11:20:51AM +0000, Daniel Stone wrote:
> > On 13 February 2017 at 10:54, Maxime Ripard wrote:
> >> On Sun, Feb 12, 2017 at 02:28:11PM +0200, Laurent Pinchart wrote:
> >>> On Thursday 02 Feb 2017 11:31:56 Maxime Ripard wrote:
> >>>> This patch add a config to support to create multi buffer for cma
> >>>> fbdev. Such as double buffer and triple buffer.
> >>>> 
> >>>> Cma fbdev is convient to add a legency fbdev. And still many Android
> >>>> devices use fbdev now and at least double buffer is needed for these
> >>>> Android devices, so that a buffer flip can be operated. It will need
> >>>> some time for Android device vendors to abondon legency fbdev. So
> >>>> multi buffer for fbdev is needed.
> >>> 
> >>> How exactly do we expect Android to move away from fbdev if we add
> >>> features to the fbdev compat layer ? I'd much rather make it clear to
> >>> them that fbdev is a thing from the past and that they'd better
> >>> migrate now.
> >> 
> >> If your point is that merging this patch will slow down the Android
> >> move away from fbdev, I disagree with that (obviously).
> >> 
> >> I don't care at all about Android on my platform of choice, but don't
> >> see how that merging this patch will change anything.
> >> 
> >> Let's be honest, Android trees typically have thousands of patches on
> >> top of mainline. Do you think a simple, 15 LoC, patch will make any
> >> difference to vendors? If they want to stay on fbdev and have that
> >> feature, they'll just merge this patch, done.
> > 
> > So, in that case, why not just let them do that? They'd already have
> > to add patches to use this, surely; we don't have anything in mainline
> > kernels which allows people to actually use this larger allocation.
> > Apart from software mmap() and using panning to do flips, but I'm
> > taking it as a given that people shipping Android on their devices
> > aren't using software rendering.
> 
> I think we need to make a distinction between fbdev the subsystem in the
> kernel, and fbdev the uabi:
> 
> - fbdev the subsystem is completely dead in upstream. I think we have full
>   agreement on that.
> - fbdev the uabi isn't, and if we can get more users from fbdev based
>   drivers to kms/atomic drivers by adding fairly simple stuff like this,
>   I'm all for it.

The real question, in my opinion, is how to get more users for the DRM/KMS 
userspace API, to help killing the fbdev API. What's the incentive for 
userspace to migrate if we tell them that we're going to support the fbdev API 
forever, and will even go through the trouble of extending the supported 
feature set ? I have a customer who wouldn't have migrated their userspace to 
DRM/KMS if these two patches had been merged a few years ago. I'd rather 
*reduce* the supported feature set over time until we can finally switch fbdev 
off.

> Which means: Yes, I fully plan to merge this, it makes sense. It even
> _helps_ by making fbdev-the-subsystem even deader. Making live hard for
> out-of-tree folks or folks with shit userspace doesn't make sense, at
> least if the only benefit for us is that we'll feel pure about our
> intentions :-)

-- 
Regards,

Laurent Pinchart

_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
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Re: [PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Maxime Ripard]

[-- Attachment #1: Type: text/plain, Size: 4407 bytes --]

Hi,

On Tue, Feb 14, 2017 at 11:25:08PM +0200, Laurent Pinchart wrote:
> Hi Daniel,
> 
> On Tuesday 14 Feb 2017 21:09:51 Daniel Vetter wrote:
> > On Mon, Feb 13, 2017 at 11:20:51AM +0000, Daniel Stone wrote:
> > > On 13 February 2017 at 10:54, Maxime Ripard wrote:
> > >> On Sun, Feb 12, 2017 at 02:28:11PM +0200, Laurent Pinchart wrote:
> > >>> On Thursday 02 Feb 2017 11:31:56 Maxime Ripard wrote:
> > >>>> This patch add a config to support to create multi buffer for cma
> > >>>> fbdev. Such as double buffer and triple buffer.
> > >>>> 
> > >>>> Cma fbdev is convient to add a legency fbdev. And still many Android
> > >>>> devices use fbdev now and at least double buffer is needed for these
> > >>>> Android devices, so that a buffer flip can be operated. It will need
> > >>>> some time for Android device vendors to abondon legency fbdev. So
> > >>>> multi buffer for fbdev is needed.
> > >>> 
> > >>> How exactly do we expect Android to move away from fbdev if we add
> > >>> features to the fbdev compat layer ? I'd much rather make it clear to
> > >>> them that fbdev is a thing from the past and that they'd better
> > >>> migrate now.
> > >> 
> > >> If your point is that merging this patch will slow down the Android
> > >> move away from fbdev, I disagree with that (obviously).
> > >> 
> > >> I don't care at all about Android on my platform of choice, but don't
> > >> see how that merging this patch will change anything.
> > >> 
> > >> Let's be honest, Android trees typically have thousands of patches on
> > >> top of mainline. Do you think a simple, 15 LoC, patch will make any
> > >> difference to vendors? If they want to stay on fbdev and have that
> > >> feature, they'll just merge this patch, done.
> > > 
> > > So, in that case, why not just let them do that? They'd already have
> > > to add patches to use this, surely; we don't have anything in mainline
> > > kernels which allows people to actually use this larger allocation.
> > > Apart from software mmap() and using panning to do flips, but I'm
> > > taking it as a given that people shipping Android on their devices
> > > aren't using software rendering.
> > 
> > I think we need to make a distinction between fbdev the subsystem in the
> > kernel, and fbdev the uabi:
> > 
> > - fbdev the subsystem is completely dead in upstream. I think we have full
> >   agreement on that.
> > - fbdev the uabi isn't, and if we can get more users from fbdev based
> >   drivers to kms/atomic drivers by adding fairly simple stuff like this,
> >   I'm all for it.
>
> The real question, in my opinion, is how to get more users for the DRM/KMS 
> userspace API, to help killing the fbdev API. What's the incentive for 
> userspace to migrate if we tell them that we're going to support the fbdev API 
> forever, and will even go through the trouble of extending the supported 
> feature set ? I have a customer who wouldn't have migrated their userspace to 
> DRM/KMS if these two patches had been merged a few years ago.

If those patches are not in, then I can see three ways to support old
/ deficient userspaces:
  1) Carry those patches out of tree
  2) Write an fbdev driver for the display engine
  3) Rewrite the userspace components

While 3. would arguably be the best option, this isn't always one,
unfortunately.

And as a community, I think 1 and 2 are not very good for us. 1. will
drive away vendors from our community, undermining the effort we've
been doing for a few years. And 2 will result in a driver we really
don't want to merge (so useless), and even if it would out of tree,
that would make it one less system / board / SoC *with* DRM/KMS APIs,
reducing the interest of switching for application developpers.

If we really want to make people switch to DRM / KMS, we have to make
it ubiquitous. And if we want to make it ubiquitous, we really want to
have a transition period where people will have both APIs, supported
in a decent enough way.

And then, that's a win for everyone, because in the process you get
fbdev (booo!) and KMS (yay!), allowing for people to switch over, and
eventually kill the emulation entirely. But it's far too early for
that. I mean, we don't even have an fbv replacement yet...

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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Re: [PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Maxime Ripard]

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Hi,

On Tue, Feb 14, 2017 at 11:25:08PM +0200, Laurent Pinchart wrote:
> Hi Daniel,
> 
> On Tuesday 14 Feb 2017 21:09:51 Daniel Vetter wrote:
> > On Mon, Feb 13, 2017 at 11:20:51AM +0000, Daniel Stone wrote:
> > > On 13 February 2017 at 10:54, Maxime Ripard wrote:
> > >> On Sun, Feb 12, 2017 at 02:28:11PM +0200, Laurent Pinchart wrote:
> > >>> On Thursday 02 Feb 2017 11:31:56 Maxime Ripard wrote:
> > >>>> This patch add a config to support to create multi buffer for cma
> > >>>> fbdev. Such as double buffer and triple buffer.
> > >>>> 
> > >>>> Cma fbdev is convient to add a legency fbdev. And still many Android
> > >>>> devices use fbdev now and at least double buffer is needed for these
> > >>>> Android devices, so that a buffer flip can be operated. It will need
> > >>>> some time for Android device vendors to abondon legency fbdev. So
> > >>>> multi buffer for fbdev is needed.
> > >>> 
> > >>> How exactly do we expect Android to move away from fbdev if we add
> > >>> features to the fbdev compat layer ? I'd much rather make it clear to
> > >>> them that fbdev is a thing from the past and that they'd better
> > >>> migrate now.
> > >> 
> > >> If your point is that merging this patch will slow down the Android
> > >> move away from fbdev, I disagree with that (obviously).
> > >> 
> > >> I don't care at all about Android on my platform of choice, but don't
> > >> see how that merging this patch will change anything.
> > >> 
> > >> Let's be honest, Android trees typically have thousands of patches on
> > >> top of mainline. Do you think a simple, 15 LoC, patch will make any
> > >> difference to vendors? If they want to stay on fbdev and have that
> > >> feature, they'll just merge this patch, done.
> > > 
> > > So, in that case, why not just let them do that? They'd already have
> > > to add patches to use this, surely; we don't have anything in mainline
> > > kernels which allows people to actually use this larger allocation.
> > > Apart from software mmap() and using panning to do flips, but I'm
> > > taking it as a given that people shipping Android on their devices
> > > aren't using software rendering.
> > 
> > I think we need to make a distinction between fbdev the subsystem in the
> > kernel, and fbdev the uabi:
> > 
> > - fbdev the subsystem is completely dead in upstream. I think we have full
> >   agreement on that.
> > - fbdev the uabi isn't, and if we can get more users from fbdev based
> >   drivers to kms/atomic drivers by adding fairly simple stuff like this,
> >   I'm all for it.
>
> The real question, in my opinion, is how to get more users for the DRM/KMS 
> userspace API, to help killing the fbdev API. What's the incentive for 
> userspace to migrate if we tell them that we're going to support the fbdev API 
> forever, and will even go through the trouble of extending the supported 
> feature set ? I have a customer who wouldn't have migrated their userspace to 
> DRM/KMS if these two patches had been merged a few years ago.

If those patches are not in, then I can see three ways to support old
/ deficient userspaces:
  1) Carry those patches out of tree
  2) Write an fbdev driver for the display engine
  3) Rewrite the userspace components

While 3. would arguably be the best option, this isn't always one,
unfortunately.

And as a community, I think 1 and 2 are not very good for us. 1. will
drive away vendors from our community, undermining the effort we've
been doing for a few years. And 2 will result in a driver we really
don't want to merge (so useless), and even if it would out of tree,
that would make it one less system / board / SoC *with* DRM/KMS APIs,
reducing the interest of switching for application developpers.

If we really want to make people switch to DRM / KMS, we have to make
it ubiquitous. And if we want to make it ubiquitous, we really want to
have a transition period where people will have both APIs, supported
in a decent enough way.

And then, that's a win for everyone, because in the process you get
fbdev (booo!) and KMS (yay!), allowing for people to switch over, and
eventually kill the emulation entirely. But it's far too early for
that. I mean, we don't even have an fbv replacement yet...

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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Re: [PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Laurent Pinchart]

Hi Maxime,

On Wednesday 15 Feb 2017 13:51:29 Maxime Ripard wrote:
> On Tue, Feb 14, 2017 at 11:25:08PM +0200, Laurent Pinchart wrote:
> > On Tuesday 14 Feb 2017 21:09:51 Daniel Vetter wrote:
> >> On Mon, Feb 13, 2017 at 11:20:51AM +0000, Daniel Stone wrote:
> >>> On 13 February 2017 at 10:54, Maxime Ripard wrote:
> >>>> On Sun, Feb 12, 2017 at 02:28:11PM +0200, Laurent Pinchart wrote:
> >>>>> On Thursday 02 Feb 2017 11:31:56 Maxime Ripard wrote:
> >>>>>> This patch add a config to support to create multi buffer for cma
> >>>>>> fbdev. Such as double buffer and triple buffer.
> >>>>>> 
> >>>>>> Cma fbdev is convient to add a legency fbdev. And still many
> >>>>>> Android devices use fbdev now and at least double buffer is needed
> >>>>>> for these Android devices, so that a buffer flip can be operated. It
> >>>>>> will need some time for Android device vendors to abondon legency
> >>>>>> fbdev. So multi buffer for fbdev is needed.
> >>>>> 
> >>>>> How exactly do we expect Android to move away from fbdev if we add
> >>>>> features to the fbdev compat layer ? I'd much rather make it clear
> >>>>> to them that fbdev is a thing from the past and that they'd better
> >>>>> migrate now.
> >>>> 
> >>>> If your point is that merging this patch will slow down the Android
> >>>> move away from fbdev, I disagree with that (obviously).
> >>>> 
> >>>> I don't care at all about Android on my platform of choice, but don't
> >>>> see how that merging this patch will change anything.
> >>>> 
> >>>> Let's be honest, Android trees typically have thousands of patches on
> >>>> top of mainline. Do you think a simple, 15 LoC, patch will make any
> >>>> difference to vendors? If they want to stay on fbdev and have that
> >>>> feature, they'll just merge this patch, done.
> >>> 
> >>> So, in that case, why not just let them do that? They'd already have
> >>> to add patches to use this, surely; we don't have anything in mainline
> >>> kernels which allows people to actually use this larger allocation.
> >>> Apart from software mmap() and using panning to do flips, but I'm
> >>> taking it as a given that people shipping Android on their devices
> >>> aren't using software rendering.
> >> 
> >> I think we need to make a distinction between fbdev the subsystem in the
> >> kernel, and fbdev the uabi:
> >> 
> >> - fbdev the subsystem is completely dead in upstream. I think we have
> >>   full agreement on that.
> >> 
> >> - fbdev the uabi isn't, and if we can get more users from fbdev based
> >>   drivers to kms/atomic drivers by adding fairly simple stuff like this,
> >>   I'm all for it.
> > 
> > The real question, in my opinion, is how to get more users for the DRM/KMS
> > userspace API, to help killing the fbdev API. What's the incentive for
> > userspace to migrate if we tell them that we're going to support the fbdev
> > API forever, and will even go through the trouble of extending the
> > supported feature set ? I have a customer who wouldn't have migrated
> > their userspace to DRM/KMS if these two patches had been merged a few
> > years ago.
> 
> If those patches are not in, then I can see three ways to support old
> / deficient userspaces:
>   1) Carry those patches out of tree
>   2) Write an fbdev driver for the display engine
>   3) Rewrite the userspace components
> 
> While 3. would arguably be the best option, this isn't always one,
> unfortunately.

I agree that it's not a solution that can be deployed overnight, but it's 
clearly what we all (as in kernel community and system vendors) need to head 
towards.

> And as a community, I think 1 and 2 are not very good for us. 1. will
> drive away vendors from our community, undermining the effort we've
> been doing for a few years. And 2 will result in a driver we really
> don't want to merge (so useless), and even if it would out of tree,
> that would make it one less system / board / SoC *with* DRM/KMS APIs,
> reducing the interest of switching for application developpers.
> 
> If we really want to make people switch to DRM / KMS, we have to make
> it ubiquitous. And if we want to make it ubiquitous, we really want to
> have a transition period where people will have both APIs, supported
> in a decent enough way.

Haven't we had such a grace period already, until the fbdev subsystem stopped 
accepting new drivers ? It has hardly been an overnight switch.

> And then, that's a win for everyone, because in the process you get
> fbdev (booo!) and KMS (yay!), allowing for people to switch over, and
> eventually kill the emulation entirely. But it's far too early for
> that. I mean, we don't even have an fbv replacement yet...

We're talking about http://s-tech.elsat.net.pl/fbv/, whose latest release 
dates from 2011 ? :-)

https://github.com/tomba/kmsxx/blob/master/utils/kmsview.cpp

It won't be hard to add support for BMP, GIF, JPG or PNG.

-- 
Regards,

Laurent Pinchart

Re: [PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Maxime Ripard]

[-- Attachment #1: Type: text/plain, Size: 3483 bytes --]

Hi,

On Mon, Feb 13, 2017 at 11:20:51AM +0000, Daniel Stone wrote:
> Hi Maxime,
> 
> On 13 February 2017 at 10:54, Maxime Ripard
> <maxime.ripard@free-electrons.com> wrote:
> > On Sun, Feb 12, 2017 at 02:28:11PM +0200, Laurent Pinchart wrote:
> >> On Thursday 02 Feb 2017 11:31:56 Maxime Ripard wrote:
> >> > This patch add a config to support to create multi buffer for cma fbdev.
> >> > Such as double buffer and triple buffer.
> >> >
> >> > Cma fbdev is convient to add a legency fbdev. And still many Android
> >> > devices use fbdev now and at least double buffer is needed for these
> >> > Android devices, so that a buffer flip can be operated. It will need
> >> > some time for Android device vendors to abondon legency fbdev. So multi
> >> > buffer for fbdev is needed.
> >>
> >> How exactly do we expect Android to move away from fbdev if we add features to
> >> the fbdev compat layer ? I'd much rather make it clear to them that fbdev is a
> >> thing from the past and that they'd better migrate now.
> >
> > If your point is that merging this patch will slow down the Android
> > move away from fbdev, I disagree with that (obviously).
> >
> > I don't care at all about Android on my platform of choice, but don't
> > see how that merging this patch will change anything.
> >
> > Let's be honest, Android trees typically have thousands of patches on
> > top of mainline. Do you think a simple, 15 LoC, patch will make any
> > difference to vendors? If they want to stay on fbdev and have that
> > feature, they'll just merge this patch, done.
> 
> So, in that case, why not just let them do that? They'd already have
> to add patches to use this, surely; we don't have anything in mainline
> kernels which allows people to actually use this larger allocation.
> Apart from software mmap() and using panning to do flips, but I'm
> taking it as a given that people shipping Android on their devices
> aren't using software rendering.

My point was that you're not doing it more difficult for people not
willing to contribute upstream, you're just making it more difficult
for people who want to contribute.

The whole argument to engage vendors upstream is that we sell them
that eventually they will be able to just use whatever kernel release
is on kernel.org or in their distro of choice.

If those people depend on a feature that is entirely rejected
upstream, then they'll have to carry that patch in their tree,
creating a BSP in the process. And that reduces greatly the strength
of the "you should contribute" argument, making them less involved.

> > However, what I do see is that three different people/organisations
> > have now expressed interest in that feature, on three different
> > SoCs. If that patch needed a significant rework of the fbdev layer,
> > then yes, I might agree that it's not worth it. But in this case, it's
> > pretty trivial.
> >
> > The only people you're "punishing" here with that kind of concern are
> > the people who actually play fair and want not to have any patches and
> > everything upstream.
> 
> I would hazard a guess that most users of this have out-of-tree GPU
> drivers.

Out of tree GPU drivers, that can be distributed separately from the
kernel, just like any out of tree module can. This doesn't require any
kernel patches at all.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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Re: [PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Maxime Ripard]

[-- Attachment #1.1: Type: text/plain, Size: 3483 bytes --]

Hi,

On Mon, Feb 13, 2017 at 11:20:51AM +0000, Daniel Stone wrote:
> Hi Maxime,
> 
> On 13 February 2017 at 10:54, Maxime Ripard
> <maxime.ripard@free-electrons.com> wrote:
> > On Sun, Feb 12, 2017 at 02:28:11PM +0200, Laurent Pinchart wrote:
> >> On Thursday 02 Feb 2017 11:31:56 Maxime Ripard wrote:
> >> > This patch add a config to support to create multi buffer for cma fbdev.
> >> > Such as double buffer and triple buffer.
> >> >
> >> > Cma fbdev is convient to add a legency fbdev. And still many Android
> >> > devices use fbdev now and at least double buffer is needed for these
> >> > Android devices, so that a buffer flip can be operated. It will need
> >> > some time for Android device vendors to abondon legency fbdev. So multi
> >> > buffer for fbdev is needed.
> >>
> >> How exactly do we expect Android to move away from fbdev if we add features to
> >> the fbdev compat layer ? I'd much rather make it clear to them that fbdev is a
> >> thing from the past and that they'd better migrate now.
> >
> > If your point is that merging this patch will slow down the Android
> > move away from fbdev, I disagree with that (obviously).
> >
> > I don't care at all about Android on my platform of choice, but don't
> > see how that merging this patch will change anything.
> >
> > Let's be honest, Android trees typically have thousands of patches on
> > top of mainline. Do you think a simple, 15 LoC, patch will make any
> > difference to vendors? If they want to stay on fbdev and have that
> > feature, they'll just merge this patch, done.
> 
> So, in that case, why not just let them do that? They'd already have
> to add patches to use this, surely; we don't have anything in mainline
> kernels which allows people to actually use this larger allocation.
> Apart from software mmap() and using panning to do flips, but I'm
> taking it as a given that people shipping Android on their devices
> aren't using software rendering.

My point was that you're not doing it more difficult for people not
willing to contribute upstream, you're just making it more difficult
for people who want to contribute.

The whole argument to engage vendors upstream is that we sell them
that eventually they will be able to just use whatever kernel release
is on kernel.org or in their distro of choice.

If those people depend on a feature that is entirely rejected
upstream, then they'll have to carry that patch in their tree,
creating a BSP in the process. And that reduces greatly the strength
of the "you should contribute" argument, making them less involved.

> > However, what I do see is that three different people/organisations
> > have now expressed interest in that feature, on three different
> > SoCs. If that patch needed a significant rework of the fbdev layer,
> > then yes, I might agree that it's not worth it. But in this case, it's
> > pretty trivial.
> >
> > The only people you're "punishing" here with that kind of concern are
> > the people who actually play fair and want not to have any patches and
> > everything upstream.
> 
> I would hazard a guess that most users of this have out-of-tree GPU
> drivers.

Out of tree GPU drivers, that can be distributed separately from the
kernel, just like any out of tree module can. This doesn't require any
kernel patches at all.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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Re: [PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Laurent Pinchart]

Hi Maxime,

On Wednesday 15 Feb 2017 13:38:44 Maxime Ripard wrote:
> On Mon, Feb 13, 2017 at 11:20:51AM +0000, Daniel Stone wrote:
> > On 13 February 2017 at 10:54, Maxime Ripard wrote:
> >> On Sun, Feb 12, 2017 at 02:28:11PM +0200, Laurent Pinchart wrote:
> >>> On Thursday 02 Feb 2017 11:31:56 Maxime Ripard wrote:
> >>>> This patch add a config to support to create multi buffer for cma
> >>>> fbdev. Such as double buffer and triple buffer.
> >>>> 
> >>>> Cma fbdev is convient to add a legency fbdev. And still many Android
> >>>> devices use fbdev now and at least double buffer is needed for these
> >>>> Android devices, so that a buffer flip can be operated. It will need
> >>>> some time for Android device vendors to abondon legency fbdev. So
> >>>> multi buffer for fbdev is needed.
> >>> 
> >>> How exactly do we expect Android to move away from fbdev if we add
> >>> features to the fbdev compat layer ? I'd much rather make it clear to
> >>> them that fbdev is a thing from the past and that they'd better
> >>> migrate now.
> >> 
> >> If your point is that merging this patch will slow down the Android
> >> move away from fbdev, I disagree with that (obviously).
> >> 
> >> I don't care at all about Android on my platform of choice, but don't
> >> see how that merging this patch will change anything.
> >> 
> >> Let's be honest, Android trees typically have thousands of patches on
> >> top of mainline. Do you think a simple, 15 LoC, patch will make any
> >> difference to vendors? If they want to stay on fbdev and have that
> >> feature, they'll just merge this patch, done.
> > 
> > So, in that case, why not just let them do that? They'd already have
> > to add patches to use this, surely; we don't have anything in mainline
> > kernels which allows people to actually use this larger allocation.
> > Apart from software mmap() and using panning to do flips, but I'm
> > taking it as a given that people shipping Android on their devices
> > aren't using software rendering.
> 
> My point was that you're not doing it more difficult for people not
> willing to contribute upstream, you're just making it more difficult
> for people who want to contribute.
> 
> The whole argument to engage vendors upstream is that we sell them
> that eventually they will be able to just use whatever kernel release
> is on kernel.org or in their distro of choice.
> 
> If those people depend on a feature that is entirely rejected
> upstream, then they'll have to carry that patch in their tree,
> creating a BSP in the process. And that reduces greatly the strength
> of the "you should contribute" argument, making them less involved.

No, they should not carry an out-of-tree patch, they should not use that 
feature in the first place. fbdev is a dead-end, Linux has clearly decided to 
move to DRM/KMS. Any vendor who wants to keep using fbdev is shooting 
themselves in the foot, as the more they depend on fbdev, the more painful it 
will be to switch later when they will have no choice. Switching sooner than 
later is the best decision, and I'd argue that by making it easier to stay on 
fbdev we would actually hurt those vendors in the longer term.

> >> However, what I do see is that three different people/organisations
> >> have now expressed interest in that feature, on three different
> >> SoCs. If that patch needed a significant rework of the fbdev layer,
> >> then yes, I might agree that it's not worth it. But in this case, it's
> >> pretty trivial.
> >> 
> >> The only people you're "punishing" here with that kind of concern are
> >> the people who actually play fair and want not to have any patches and
> >> everything upstream.
> > 
> > I would hazard a guess that most users of this have out-of-tree GPU
> > drivers.
> 
> Out of tree GPU drivers, that can be distributed separately from the
> kernel, just like any out of tree module can. This doesn't require any
> kernel patches at all.

That might be true in some cases, but usually those GPU drivers require heavy 
patching of at least the display controller driver.

-- 
Regards,

Laurent Pinchart

Re: [PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Laurent Pinchart]

Hi Maxime,

On Wednesday 15 Feb 2017 13:38:44 Maxime Ripard wrote:
> On Mon, Feb 13, 2017 at 11:20:51AM +0000, Daniel Stone wrote:
> > On 13 February 2017 at 10:54, Maxime Ripard wrote:
> >> On Sun, Feb 12, 2017 at 02:28:11PM +0200, Laurent Pinchart wrote:
> >>> On Thursday 02 Feb 2017 11:31:56 Maxime Ripard wrote:
> >>>> This patch add a config to support to create multi buffer for cma
> >>>> fbdev. Such as double buffer and triple buffer.
> >>>> 
> >>>> Cma fbdev is convient to add a legency fbdev. And still many Android
> >>>> devices use fbdev now and at least double buffer is needed for these
> >>>> Android devices, so that a buffer flip can be operated. It will need
> >>>> some time for Android device vendors to abondon legency fbdev. So
> >>>> multi buffer for fbdev is needed.
> >>> 
> >>> How exactly do we expect Android to move away from fbdev if we add
> >>> features to the fbdev compat layer ? I'd much rather make it clear to
> >>> them that fbdev is a thing from the past and that they'd better
> >>> migrate now.
> >> 
> >> If your point is that merging this patch will slow down the Android
> >> move away from fbdev, I disagree with that (obviously).
> >> 
> >> I don't care at all about Android on my platform of choice, but don't
> >> see how that merging this patch will change anything.
> >> 
> >> Let's be honest, Android trees typically have thousands of patches on
> >> top of mainline. Do you think a simple, 15 LoC, patch will make any
> >> difference to vendors? If they want to stay on fbdev and have that
> >> feature, they'll just merge this patch, done.
> > 
> > So, in that case, why not just let them do that? They'd already have
> > to add patches to use this, surely; we don't have anything in mainline
> > kernels which allows people to actually use this larger allocation.
> > Apart from software mmap() and using panning to do flips, but I'm
> > taking it as a given that people shipping Android on their devices
> > aren't using software rendering.
> 
> My point was that you're not doing it more difficult for people not
> willing to contribute upstream, you're just making it more difficult
> for people who want to contribute.
> 
> The whole argument to engage vendors upstream is that we sell them
> that eventually they will be able to just use whatever kernel release
> is on kernel.org or in their distro of choice.
> 
> If those people depend on a feature that is entirely rejected
> upstream, then they'll have to carry that patch in their tree,
> creating a BSP in the process. And that reduces greatly the strength
> of the "you should contribute" argument, making them less involved.

No, they should not carry an out-of-tree patch, they should not use that 
feature in the first place. fbdev is a dead-end, Linux has clearly decided to 
move to DRM/KMS. Any vendor who wants to keep using fbdev is shooting 
themselves in the foot, as the more they depend on fbdev, the more painful it 
will be to switch later when they will have no choice. Switching sooner than 
later is the best decision, and I'd argue that by making it easier to stay on 
fbdev we would actually hurt those vendors in the longer term.

> >> However, what I do see is that three different people/organisations
> >> have now expressed interest in that feature, on three different
> >> SoCs. If that patch needed a significant rework of the fbdev layer,
> >> then yes, I might agree that it's not worth it. But in this case, it's
> >> pretty trivial.
> >> 
> >> The only people you're "punishing" here with that kind of concern are
> >> the people who actually play fair and want not to have any patches and
> >> everything upstream.
> > 
> > I would hazard a guess that most users of this have out-of-tree GPU
> > drivers.
> 
> Out of tree GPU drivers, that can be distributed separately from the
> kernel, just like any out of tree module can. This doesn't require any
> kernel patches at all.

That might be true in some cases, but usually those GPU drivers require heavy 
patching of at least the display controller driver.

-- 
Regards,

Laurent Pinchart

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dri-devel@lists.freedesktop.org
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[PATCH v2 2/2] drm/fb_helper: implement ioctl FBIO_WAITFORVSYNC

[Maxime Ripard]

From: Stefan Christ <s.christ@phytec.de>

Implement legacy framebuffer ioctl FBIO_WAITFORVSYNC in the generic
framebuffer emulation driver. Legacy framebuffer users like non kms/drm
based OpenGL(ES)/EGL implementations may require the ioctl to
synchronize drawing or buffer flip for double buffering. It is tested on
the i.MX6.

Code is based on
    https://github.com/Xilinx/linux-xlnx/blob/master/drivers/gpu/drm/xilinx/xilinx_drm_fb.c#L196

Signed-off-by: Stefan Christ <s.christ@phytec.de>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
---
 drivers/gpu/drm/drm_fb_helper.c | 55 ++++++++++++++++++++++++++++++++++-
 include/drm/drm_fb_helper.h     |  5 ++-
 2 files changed, 59 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index e934b541feea..39a3532e311c 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -1234,6 +1234,61 @@ int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
 EXPORT_SYMBOL(drm_fb_helper_setcmap);
 
 /**
+ * drm_fb_helper_ioctl - legacy ioctl implementation
+ * @info: fbdev registered by the helper
+ * @cmd: ioctl command
+ * @arg: ioctl argument
+ *
+ * A helper to implement the standard fbdev ioctl. Only
+ * FBIO_WAITFORVSYNC is implemented for now.
+ */
+int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg)
+{
+	struct drm_fb_helper *fb_helper = info->par;
+	struct drm_device *dev = fb_helper->dev;
+	unsigned int i;
+	int ret = 0;
+
+	drm_modeset_lock_all(dev);
+	if (!drm_fb_helper_is_bound(fb_helper)) {
+		drm_modeset_unlock_all(dev);
+		return -EBUSY;
+	}
+
+	switch (cmd) {
+	case FBIO_WAITFORVSYNC:
+		for (i = 0; i < fb_helper->crtc_count; i++) {
+			struct drm_mode_set *mode_set;
+			struct drm_crtc *crtc;
+
+			mode_set = &fb_helper->crtc_info[i].mode_set;
+			crtc = mode_set->crtc;
+
+			/*
+			 * Only call drm_crtc_wait_one_vblank for crtcs that
+			 * are currently enabled.
+			 */
+			if (!crtc->enabled)
+				continue;
+
+			ret = drm_crtc_vblank_get(crtc);
+			if (!ret) {
+				drm_crtc_wait_one_vblank(crtc);
+				drm_crtc_vblank_put(crtc);
+			}
+		}
+		goto unlock;
+	default:
+		ret = -ENOTTY;
+	}
+
+unlock:
+	drm_modeset_unlock_all(dev);
+	return ret;
+}
+EXPORT_SYMBOL(drm_fb_helper_ioctl);
+
+/**
  * drm_fb_helper_check_var - implementation for ->fb_check_var
  * @var: screeninfo to check
  * @info: fbdev registered by the helper
diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
index 975deedd593e..460be9d9fa98 100644
--- a/include/drm/drm_fb_helper.h
+++ b/include/drm/drm_fb_helper.h
@@ -230,7 +230,8 @@ struct drm_fb_helper {
 	.fb_blank	= drm_fb_helper_blank, \
 	.fb_pan_display	= drm_fb_helper_pan_display, \
 	.fb_debug_enter = drm_fb_helper_debug_enter, \
-	.fb_debug_leave = drm_fb_helper_debug_leave
+	.fb_debug_leave = drm_fb_helper_debug_leave, \
+	.fb_ioctl	= drm_fb_helper_ioctl
 
 #ifdef CONFIG_DRM_FBDEV_EMULATION
 void drm_fb_helper_prepare(struct drm_device *dev, struct drm_fb_helper *helper,
@@ -286,6 +287,8 @@ void drm_fb_helper_set_suspend_unlocked(struct drm_fb_helper *fb_helper,
 
 int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info);
 
+int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg);
+
 int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper);
 int drm_fb_helper_initial_config(struct drm_fb_helper *fb_helper, int bpp_sel);
 int drm_fb_helper_single_add_all_connectors(struct drm_fb_helper *fb_helper);
-- 
git-series 0.8.11

[PATCH v2 2/2] drm/fb_helper: implement ioctl FBIO_WAITFORVSYNC

[Maxime Ripard]

From: Stefan Christ <s.christ@phytec.de>

Implement legacy framebuffer ioctl FBIO_WAITFORVSYNC in the generic
framebuffer emulation driver. Legacy framebuffer users like non kms/drm
based OpenGL(ES)/EGL implementations may require the ioctl to
synchronize drawing or buffer flip for double buffering. It is tested on
the i.MX6.

Code is based on
    https://github.com/Xilinx/linux-xlnx/blob/master/drivers/gpu/drm/xilinx/xilinx_drm_fb.c#L196

Signed-off-by: Stefan Christ <s.christ@phytec.de>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
---
 drivers/gpu/drm/drm_fb_helper.c | 55 ++++++++++++++++++++++++++++++++++-
 include/drm/drm_fb_helper.h     |  5 ++-
 2 files changed, 59 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index e934b541feea..39a3532e311c 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -1234,6 +1234,61 @@ int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
 EXPORT_SYMBOL(drm_fb_helper_setcmap);
 
 /**
+ * drm_fb_helper_ioctl - legacy ioctl implementation
+ * @info: fbdev registered by the helper
+ * @cmd: ioctl command
+ * @arg: ioctl argument
+ *
+ * A helper to implement the standard fbdev ioctl. Only
+ * FBIO_WAITFORVSYNC is implemented for now.
+ */
+int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg)
+{
+	struct drm_fb_helper *fb_helper = info->par;
+	struct drm_device *dev = fb_helper->dev;
+	unsigned int i;
+	int ret = 0;
+
+	drm_modeset_lock_all(dev);
+	if (!drm_fb_helper_is_bound(fb_helper)) {
+		drm_modeset_unlock_all(dev);
+		return -EBUSY;
+	}
+
+	switch (cmd) {
+	case FBIO_WAITFORVSYNC:
+		for (i = 0; i < fb_helper->crtc_count; i++) {
+			struct drm_mode_set *mode_set;
+			struct drm_crtc *crtc;
+
+			mode_set = &fb_helper->crtc_info[i].mode_set;
+			crtc = mode_set->crtc;
+
+			/*
+			 * Only call drm_crtc_wait_one_vblank for crtcs that
+			 * are currently enabled.
+			 */
+			if (!crtc->enabled)
+				continue;
+
+			ret = drm_crtc_vblank_get(crtc);
+			if (!ret) {
+				drm_crtc_wait_one_vblank(crtc);
+				drm_crtc_vblank_put(crtc);
+			}
+		}
+		goto unlock;
+	default:
+		ret = -ENOTTY;
+	}
+
+unlock:
+	drm_modeset_unlock_all(dev);
+	return ret;
+}
+EXPORT_SYMBOL(drm_fb_helper_ioctl);
+
+/**
  * drm_fb_helper_check_var - implementation for ->fb_check_var
  * @var: screeninfo to check
  * @info: fbdev registered by the helper
diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
index 975deedd593e..460be9d9fa98 100644
--- a/include/drm/drm_fb_helper.h
+++ b/include/drm/drm_fb_helper.h
@@ -230,7 +230,8 @@ struct drm_fb_helper {
 	.fb_blank	= drm_fb_helper_blank, \
 	.fb_pan_display	= drm_fb_helper_pan_display, \
 	.fb_debug_enter = drm_fb_helper_debug_enter, \
-	.fb_debug_leave = drm_fb_helper_debug_leave
+	.fb_debug_leave = drm_fb_helper_debug_leave, \
+	.fb_ioctl	= drm_fb_helper_ioctl
 
 #ifdef CONFIG_DRM_FBDEV_EMULATION
 void drm_fb_helper_prepare(struct drm_device *dev, struct drm_fb_helper *helper,
@@ -286,6 +287,8 @@ void drm_fb_helper_set_suspend_unlocked(struct drm_fb_helper *fb_helper,
 
 int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info);
 
+int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg);
+
 int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper);
 int drm_fb_helper_initial_config(struct drm_fb_helper *fb_helper, int bpp_sel);
 int drm_fb_helper_single_add_all_connectors(struct drm_fb_helper *fb_helper);
-- 
git-series 0.8.11
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Re: [PATCH v2 2/2] drm/fb_helper: implement ioctl FBIO_WAITFORVSYNC

[Daniel Vetter]

On Thu, Feb 02, 2017 at 11:31:57AM +0100, Maxime Ripard wrote:
> From: Stefan Christ <s.christ@phytec.de>
> 
> Implement legacy framebuffer ioctl FBIO_WAITFORVSYNC in the generic
> framebuffer emulation driver. Legacy framebuffer users like non kms/drm
> based OpenGL(ES)/EGL implementations may require the ioctl to
> synchronize drawing or buffer flip for double buffering. It is tested on
> the i.MX6.
> 
> Code is based on
>     https://github.com/Xilinx/linux-xlnx/blob/master/drivers/gpu/drm/xilinx/xilinx_drm_fb.c#L196
> 
> Signed-off-by: Stefan Christ <s.christ@phytec.de>
> Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> ---
>  drivers/gpu/drm/drm_fb_helper.c | 55 ++++++++++++++++++++++++++++++++++-
>  include/drm/drm_fb_helper.h     |  5 ++-
>  2 files changed, 59 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index e934b541feea..39a3532e311c 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -1234,6 +1234,61 @@ int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
>  EXPORT_SYMBOL(drm_fb_helper_setcmap);
>  
>  /**
> + * drm_fb_helper_ioctl - legacy ioctl implementation
> + * @info: fbdev registered by the helper
> + * @cmd: ioctl command
> + * @arg: ioctl argument
> + *
> + * A helper to implement the standard fbdev ioctl. Only
> + * FBIO_WAITFORVSYNC is implemented for now.
> + */
> +int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg)
> +{
> +	struct drm_fb_helper *fb_helper = info->par;
> +	struct drm_device *dev = fb_helper->dev;
> +	unsigned int i;
> +	int ret = 0;
> +
> +	drm_modeset_lock_all(dev);
> +	if (!drm_fb_helper_is_bound(fb_helper)) {
> +		drm_modeset_unlock_all(dev);
> +		return -EBUSY;
> +	}
> +
> +	switch (cmd) {
> +	case FBIO_WAITFORVSYNC:
> +		for (i = 0; i < fb_helper->crtc_count; i++) {
> +			struct drm_mode_set *mode_set;
> +			struct drm_crtc *crtc;
> +
> +			mode_set = &fb_helper->crtc_info[i].mode_set;
> +			crtc = mode_set->crtc;
> +
> +			/*
> +			 * Only call drm_crtc_wait_one_vblank for crtcs that
> +			 * are currently enabled.
> +			 */
> +			if (!crtc->enabled)
> +				continue;

This needs locking, and the interface spec for vblank_get says you'll get
an -EINVAL if the pipe is off. I'd say drop this, and instead eat the
-EINVAL from vblank_get and explain in a comment why you do that.

The trouble is that ->enabled is legacy state, atomic drivers don't need
to update it (helpers do it by default, but only for transition reasons),
and it's not synchronized to the real state changes at all. vblank_get
otoh is.

Otherwise lgtm.
-Daniel

> +
> +			ret = drm_crtc_vblank_get(crtc);
> +			if (!ret) {
> +				drm_crtc_wait_one_vblank(crtc);
> +				drm_crtc_vblank_put(crtc);
> +			}
> +		}
> +		goto unlock;
> +	default:
> +		ret = -ENOTTY;
> +	}
> +
> +unlock:
> +	drm_modeset_unlock_all(dev);
> +	return ret;
> +}
> +EXPORT_SYMBOL(drm_fb_helper_ioctl);
> +
> +/**
>   * drm_fb_helper_check_var - implementation for ->fb_check_var
>   * @var: screeninfo to check
>   * @info: fbdev registered by the helper
> diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
> index 975deedd593e..460be9d9fa98 100644
> --- a/include/drm/drm_fb_helper.h
> +++ b/include/drm/drm_fb_helper.h
> @@ -230,7 +230,8 @@ struct drm_fb_helper {
>  	.fb_blank	= drm_fb_helper_blank, \
>  	.fb_pan_display	= drm_fb_helper_pan_display, \
>  	.fb_debug_enter = drm_fb_helper_debug_enter, \
> -	.fb_debug_leave = drm_fb_helper_debug_leave
> +	.fb_debug_leave = drm_fb_helper_debug_leave, \
> +	.fb_ioctl	= drm_fb_helper_ioctl
>  
>  #ifdef CONFIG_DRM_FBDEV_EMULATION
>  void drm_fb_helper_prepare(struct drm_device *dev, struct drm_fb_helper *helper,
> @@ -286,6 +287,8 @@ void drm_fb_helper_set_suspend_unlocked(struct drm_fb_helper *fb_helper,
>  
>  int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info);
>  
> +int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg);
> +
>  int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper);
>  int drm_fb_helper_initial_config(struct drm_fb_helper *fb_helper, int bpp_sel);
>  int drm_fb_helper_single_add_all_connectors(struct drm_fb_helper *fb_helper);
> -- 
> git-series 0.8.11
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

Re: [PATCH v2 2/2] drm/fb_helper: implement ioctl FBIO_WAITFORVSYNC

[Daniel Vetter]

On Thu, Feb 02, 2017 at 11:31:57AM +0100, Maxime Ripard wrote:
> From: Stefan Christ <s.christ@phytec.de>
> 
> Implement legacy framebuffer ioctl FBIO_WAITFORVSYNC in the generic
> framebuffer emulation driver. Legacy framebuffer users like non kms/drm
> based OpenGL(ES)/EGL implementations may require the ioctl to
> synchronize drawing or buffer flip for double buffering. It is tested on
> the i.MX6.
> 
> Code is based on
>     https://github.com/Xilinx/linux-xlnx/blob/master/drivers/gpu/drm/xilinx/xilinx_drm_fb.c#L196
> 
> Signed-off-by: Stefan Christ <s.christ@phytec.de>
> Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> ---
>  drivers/gpu/drm/drm_fb_helper.c | 55 ++++++++++++++++++++++++++++++++++-
>  include/drm/drm_fb_helper.h     |  5 ++-
>  2 files changed, 59 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index e934b541feea..39a3532e311c 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -1234,6 +1234,61 @@ int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
>  EXPORT_SYMBOL(drm_fb_helper_setcmap);
>  
>  /**
> + * drm_fb_helper_ioctl - legacy ioctl implementation
> + * @info: fbdev registered by the helper
> + * @cmd: ioctl command
> + * @arg: ioctl argument
> + *
> + * A helper to implement the standard fbdev ioctl. Only
> + * FBIO_WAITFORVSYNC is implemented for now.
> + */
> +int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg)
> +{
> +	struct drm_fb_helper *fb_helper = info->par;
> +	struct drm_device *dev = fb_helper->dev;
> +	unsigned int i;
> +	int ret = 0;
> +
> +	drm_modeset_lock_all(dev);
> +	if (!drm_fb_helper_is_bound(fb_helper)) {
> +		drm_modeset_unlock_all(dev);
> +		return -EBUSY;
> +	}
> +
> +	switch (cmd) {
> +	case FBIO_WAITFORVSYNC:
> +		for (i = 0; i < fb_helper->crtc_count; i++) {
> +			struct drm_mode_set *mode_set;
> +			struct drm_crtc *crtc;
> +
> +			mode_set = &fb_helper->crtc_info[i].mode_set;
> +			crtc = mode_set->crtc;
> +
> +			/*
> +			 * Only call drm_crtc_wait_one_vblank for crtcs that
> +			 * are currently enabled.
> +			 */
> +			if (!crtc->enabled)
> +				continue;

This needs locking, and the interface spec for vblank_get says you'll get
an -EINVAL if the pipe is off. I'd say drop this, and instead eat the
-EINVAL from vblank_get and explain in a comment why you do that.

The trouble is that ->enabled is legacy state, atomic drivers don't need
to update it (helpers do it by default, but only for transition reasons),
and it's not synchronized to the real state changes at all. vblank_get
otoh is.

Otherwise lgtm.
-Daniel

> +
> +			ret = drm_crtc_vblank_get(crtc);
> +			if (!ret) {
> +				drm_crtc_wait_one_vblank(crtc);
> +				drm_crtc_vblank_put(crtc);
> +			}
> +		}
> +		goto unlock;
> +	default:
> +		ret = -ENOTTY;
> +	}
> +
> +unlock:
> +	drm_modeset_unlock_all(dev);
> +	return ret;
> +}
> +EXPORT_SYMBOL(drm_fb_helper_ioctl);
> +
> +/**
>   * drm_fb_helper_check_var - implementation for ->fb_check_var
>   * @var: screeninfo to check
>   * @info: fbdev registered by the helper
> diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
> index 975deedd593e..460be9d9fa98 100644
> --- a/include/drm/drm_fb_helper.h
> +++ b/include/drm/drm_fb_helper.h
> @@ -230,7 +230,8 @@ struct drm_fb_helper {
>  	.fb_blank	= drm_fb_helper_blank, \
>  	.fb_pan_display	= drm_fb_helper_pan_display, \
>  	.fb_debug_enter = drm_fb_helper_debug_enter, \
> -	.fb_debug_leave = drm_fb_helper_debug_leave
> +	.fb_debug_leave = drm_fb_helper_debug_leave, \
> +	.fb_ioctl	= drm_fb_helper_ioctl
>  
>  #ifdef CONFIG_DRM_FBDEV_EMULATION
>  void drm_fb_helper_prepare(struct drm_device *dev, struct drm_fb_helper *helper,
> @@ -286,6 +287,8 @@ void drm_fb_helper_set_suspend_unlocked(struct drm_fb_helper *fb_helper,
>  
>  int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info);
>  
> +int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg);
> +
>  int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper);
>  int drm_fb_helper_initial_config(struct drm_fb_helper *fb_helper, int bpp_sel);
>  int drm_fb_helper_single_add_all_connectors(struct drm_fb_helper *fb_helper);
> -- 
> git-series 0.8.11
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

Re: [PATCH v2 2/2] drm/fb_helper: implement ioctl FBIO_WAITFORVSYNC

[Daniel Stone]

Hi,

On 9 February 2017 at 17:01, Daniel Vetter <daniel@ffwll.ch> wrote:
> On Thu, Feb 02, 2017 at 11:31:57AM +0100, Maxime Ripard wrote:
>> +int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg)
>> +{
>> +     struct drm_fb_helper *fb_helper = info->par;
>> +     struct drm_device *dev = fb_helper->dev;
>> +     unsigned int i;
>> +     int ret = 0;
>> +
>> +     drm_modeset_lock_all(dev);
>> +     if (!drm_fb_helper_is_bound(fb_helper)) {
>> +             drm_modeset_unlock_all(dev);
>> +             return -EBUSY;
>> +     }
>> +
>> +     switch (cmd) {
>> +     case FBIO_WAITFORVSYNC:
>> +             for (i = 0; i < fb_helper->crtc_count; i++) {
>> +                     struct drm_mode_set *mode_set;
>> +                     struct drm_crtc *crtc;
>> +
>> +                     mode_set = &fb_helper->crtc_info[i].mode_set;
>> +                     crtc = mode_set->crtc;
>> +
>> +                     /*
>> +                      * Only call drm_crtc_wait_one_vblank for crtcs that
>> +                      * are currently enabled.
>> +                      */
>> +                     if (!crtc->enabled)
>> +                             continue;
>
> This needs locking

More locking than the drm_modeset_lock_all() above the switch? Ouch. :)

Cheers,
Daniel

Re: [PATCH v2 2/2] drm/fb_helper: implement ioctl FBIO_WAITFORVSYNC

[Daniel Stone]

Hi,

On 9 February 2017 at 17:01, Daniel Vetter <daniel@ffwll.ch> wrote:
> On Thu, Feb 02, 2017 at 11:31:57AM +0100, Maxime Ripard wrote:
>> +int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg)
>> +{
>> +     struct drm_fb_helper *fb_helper = info->par;
>> +     struct drm_device *dev = fb_helper->dev;
>> +     unsigned int i;
>> +     int ret = 0;
>> +
>> +     drm_modeset_lock_all(dev);
>> +     if (!drm_fb_helper_is_bound(fb_helper)) {
>> +             drm_modeset_unlock_all(dev);
>> +             return -EBUSY;
>> +     }
>> +
>> +     switch (cmd) {
>> +     case FBIO_WAITFORVSYNC:
>> +             for (i = 0; i < fb_helper->crtc_count; i++) {
>> +                     struct drm_mode_set *mode_set;
>> +                     struct drm_crtc *crtc;
>> +
>> +                     mode_set = &fb_helper->crtc_info[i].mode_set;
>> +                     crtc = mode_set->crtc;
>> +
>> +                     /*
>> +                      * Only call drm_crtc_wait_one_vblank for crtcs that
>> +                      * are currently enabled.
>> +                      */
>> +                     if (!crtc->enabled)
>> +                             continue;
>
> This needs locking

More locking than the drm_modeset_lock_all() above the switch? Ouch. :)

Cheers,
Daniel
_______________________________________________
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https://lists.freedesktop.org/mailman/listinfo/dri-devel

Re: [PATCH v2 2/2] drm/fb_helper: implement ioctl FBIO_WAITFORVSYNC

[Daniel Vetter]

On Thu, Feb 09, 2017 at 05:38:26PM +0000, Daniel Stone wrote:
> Hi,
> 
> On 9 February 2017 at 17:01, Daniel Vetter <daniel@ffwll.ch> wrote:
> > On Thu, Feb 02, 2017 at 11:31:57AM +0100, Maxime Ripard wrote:
> >> +int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg)
> >> +{
> >> +     struct drm_fb_helper *fb_helper = info->par;
> >> +     struct drm_device *dev = fb_helper->dev;
> >> +     unsigned int i;
> >> +     int ret = 0;
> >> +
> >> +     drm_modeset_lock_all(dev);
> >> +     if (!drm_fb_helper_is_bound(fb_helper)) {
> >> +             drm_modeset_unlock_all(dev);
> >> +             return -EBUSY;
> >> +     }
> >> +
> >> +     switch (cmd) {
> >> +     case FBIO_WAITFORVSYNC:
> >> +             for (i = 0; i < fb_helper->crtc_count; i++) {
> >> +                     struct drm_mode_set *mode_set;
> >> +                     struct drm_crtc *crtc;
> >> +
> >> +                     mode_set = &fb_helper->crtc_info[i].mode_set;
> >> +                     crtc = mode_set->crtc;
> >> +
> >> +                     /*
> >> +                      * Only call drm_crtc_wait_one_vblank for crtcs that
> >> +                      * are currently enabled.
> >> +                      */
> >> +                     if (!crtc->enabled)
> >> +                             continue;
> >
> > This needs locking
> 
> More locking than the drm_modeset_lock_all() above the switch? Ouch. :)

Oh, I didn't spot that one. Well, that one should be removed imo, we dont
want any vblank wait path to hold these locks, it looks bad. Otoh we still
need to grab the dev->mode_config.mutex, because that's also the fbdev
lock. There's a plan somewhere to give the fbdev helpers their own lock,
so switching to just mode_config.mutex + the changes I suggestd would be
good.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

Re: [PATCH v2 2/2] drm/fb_helper: implement ioctl FBIO_WAITFORVSYNC

[Daniel Vetter]

On Thu, Feb 09, 2017 at 05:38:26PM +0000, Daniel Stone wrote:
> Hi,
> 
> On 9 February 2017 at 17:01, Daniel Vetter <daniel@ffwll.ch> wrote:
> > On Thu, Feb 02, 2017 at 11:31:57AM +0100, Maxime Ripard wrote:
> >> +int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg)
> >> +{
> >> +     struct drm_fb_helper *fb_helper = info->par;
> >> +     struct drm_device *dev = fb_helper->dev;
> >> +     unsigned int i;
> >> +     int ret = 0;
> >> +
> >> +     drm_modeset_lock_all(dev);
> >> +     if (!drm_fb_helper_is_bound(fb_helper)) {
> >> +             drm_modeset_unlock_all(dev);
> >> +             return -EBUSY;
> >> +     }
> >> +
> >> +     switch (cmd) {
> >> +     case FBIO_WAITFORVSYNC:
> >> +             for (i = 0; i < fb_helper->crtc_count; i++) {
> >> +                     struct drm_mode_set *mode_set;
> >> +                     struct drm_crtc *crtc;
> >> +
> >> +                     mode_set = &fb_helper->crtc_info[i].mode_set;
> >> +                     crtc = mode_set->crtc;
> >> +
> >> +                     /*
> >> +                      * Only call drm_crtc_wait_one_vblank for crtcs that
> >> +                      * are currently enabled.
> >> +                      */
> >> +                     if (!crtc->enabled)
> >> +                             continue;
> >
> > This needs locking
> 
> More locking than the drm_modeset_lock_all() above the switch? Ouch. :)

Oh, I didn't spot that one. Well, that one should be removed imo, we dont
want any vblank wait path to hold these locks, it looks bad. Otoh we still
need to grab the dev->mode_config.mutex, because that's also the fbdev
lock. There's a plan somewhere to give the fbdev helpers their own lock,
so switching to just mode_config.mutex + the changes I suggestd would be
good.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

Re: [PATCH v2 2/2] drm/fb_helper: implement ioctl FBIO_WAITFORVSYNC

[Ville Syrjälä]

On Thu, Feb 02, 2017 at 11:31:57AM +0100, Maxime Ripard wrote:
> From: Stefan Christ <s.christ@phytec.de>
> 
> Implement legacy framebuffer ioctl FBIO_WAITFORVSYNC in the generic
> framebuffer emulation driver. Legacy framebuffer users like non kms/drm
> based OpenGL(ES)/EGL implementations may require the ioctl to
> synchronize drawing or buffer flip for double buffering. It is tested on
> the i.MX6.
> 
> Code is based on
>     https://github.com/Xilinx/linux-xlnx/blob/master/drivers/gpu/drm/xilinx/xilinx_drm_fb.c#L196
> 
> Signed-off-by: Stefan Christ <s.christ@phytec.de>
> Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> ---
>  drivers/gpu/drm/drm_fb_helper.c | 55 ++++++++++++++++++++++++++++++++++-
>  include/drm/drm_fb_helper.h     |  5 ++-
>  2 files changed, 59 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index e934b541feea..39a3532e311c 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -1234,6 +1234,61 @@ int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
>  EXPORT_SYMBOL(drm_fb_helper_setcmap);
>  
>  /**
> + * drm_fb_helper_ioctl - legacy ioctl implementation
> + * @info: fbdev registered by the helper
> + * @cmd: ioctl command
> + * @arg: ioctl argument
> + *
> + * A helper to implement the standard fbdev ioctl. Only
> + * FBIO_WAITFORVSYNC is implemented for now.
> + */
> +int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg)
> +{
> +	struct drm_fb_helper *fb_helper = info->par;
> +	struct drm_device *dev = fb_helper->dev;
> +	unsigned int i;
> +	int ret = 0;
> +
> +	drm_modeset_lock_all(dev);
> +	if (!drm_fb_helper_is_bound(fb_helper)) {
> +		drm_modeset_unlock_all(dev);
> +		return -EBUSY;
> +	}
> +
> +	switch (cmd) {
> +	case FBIO_WAITFORVSYNC:
> +		for (i = 0; i < fb_helper->crtc_count; i++) {

FBIO_WAITFORVSYNC takes the crtc as a parmeter, so I'm not sure we want
to do this for all the crtcs. Though what that crtc means for fb is
rather poorly defined.

> +			struct drm_mode_set *mode_set;
> +			struct drm_crtc *crtc;
> +
> +			mode_set = &fb_helper->crtc_info[i].mode_set;
> +			crtc = mode_set->crtc;
> +
> +			/*
> +			 * Only call drm_crtc_wait_one_vblank for crtcs that
> +			 * are currently enabled.
> +			 */
> +			if (!crtc->enabled)
> +				continue;
> +
> +			ret = drm_crtc_vblank_get(crtc);
> +			if (!ret) {
> +				drm_crtc_wait_one_vblank(crtc);
> +				drm_crtc_vblank_put(crtc);
> +			}

This looks quite sub-optimal. It should rather do something along the
lines of what drm_atomic_helper_wait_for_vblanks() does.

> +		}
> +		goto unlock;
> +	default:
> +		ret = -ENOTTY;
> +	}
> +
> +unlock:
> +	drm_modeset_unlock_all(dev);
> +	return ret;
> +}
> +EXPORT_SYMBOL(drm_fb_helper_ioctl);
> +
> +/**
>   * drm_fb_helper_check_var - implementation for ->fb_check_var
>   * @var: screeninfo to check
>   * @info: fbdev registered by the helper
> diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
> index 975deedd593e..460be9d9fa98 100644
> --- a/include/drm/drm_fb_helper.h
> +++ b/include/drm/drm_fb_helper.h
> @@ -230,7 +230,8 @@ struct drm_fb_helper {
>  	.fb_blank	= drm_fb_helper_blank, \
>  	.fb_pan_display	= drm_fb_helper_pan_display, \
>  	.fb_debug_enter = drm_fb_helper_debug_enter, \
> -	.fb_debug_leave = drm_fb_helper_debug_leave
> +	.fb_debug_leave = drm_fb_helper_debug_leave, \
> +	.fb_ioctl	= drm_fb_helper_ioctl
>  
>  #ifdef CONFIG_DRM_FBDEV_EMULATION
>  void drm_fb_helper_prepare(struct drm_device *dev, struct drm_fb_helper *helper,
> @@ -286,6 +287,8 @@ void drm_fb_helper_set_suspend_unlocked(struct drm_fb_helper *fb_helper,
>  
>  int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info);
>  
> +int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg);
> +
>  int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper);
>  int drm_fb_helper_initial_config(struct drm_fb_helper *fb_helper, int bpp_sel);
>  int drm_fb_helper_single_add_all_connectors(struct drm_fb_helper *fb_helper);
> -- 
> git-series 0.8.11
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Ville Syrjälä
Intel OTC

Re: [PATCH v2 2/2] drm/fb_helper: implement ioctl FBIO_WAITFORVSYNC

[Ville Syrjälä]

On Thu, Feb 02, 2017 at 11:31:57AM +0100, Maxime Ripard wrote:
> From: Stefan Christ <s.christ@phytec.de>
> 
> Implement legacy framebuffer ioctl FBIO_WAITFORVSYNC in the generic
> framebuffer emulation driver. Legacy framebuffer users like non kms/drm
> based OpenGL(ES)/EGL implementations may require the ioctl to
> synchronize drawing or buffer flip for double buffering. It is tested on
> the i.MX6.
> 
> Code is based on
>     https://github.com/Xilinx/linux-xlnx/blob/master/drivers/gpu/drm/xilinx/xilinx_drm_fb.c#L196
> 
> Signed-off-by: Stefan Christ <s.christ@phytec.de>
> Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> ---
>  drivers/gpu/drm/drm_fb_helper.c | 55 ++++++++++++++++++++++++++++++++++-
>  include/drm/drm_fb_helper.h     |  5 ++-
>  2 files changed, 59 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index e934b541feea..39a3532e311c 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -1234,6 +1234,61 @@ int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
>  EXPORT_SYMBOL(drm_fb_helper_setcmap);
>  
>  /**
> + * drm_fb_helper_ioctl - legacy ioctl implementation
> + * @info: fbdev registered by the helper
> + * @cmd: ioctl command
> + * @arg: ioctl argument
> + *
> + * A helper to implement the standard fbdev ioctl. Only
> + * FBIO_WAITFORVSYNC is implemented for now.
> + */
> +int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg)
> +{
> +	struct drm_fb_helper *fb_helper = info->par;
> +	struct drm_device *dev = fb_helper->dev;
> +	unsigned int i;
> +	int ret = 0;
> +
> +	drm_modeset_lock_all(dev);
> +	if (!drm_fb_helper_is_bound(fb_helper)) {
> +		drm_modeset_unlock_all(dev);
> +		return -EBUSY;
> +	}
> +
> +	switch (cmd) {
> +	case FBIO_WAITFORVSYNC:
> +		for (i = 0; i < fb_helper->crtc_count; i++) {

FBIO_WAITFORVSYNC takes the crtc as a parmeter, so I'm not sure we want
to do this for all the crtcs. Though what that crtc means for fb is
rather poorly defined.

> +			struct drm_mode_set *mode_set;
> +			struct drm_crtc *crtc;
> +
> +			mode_set = &fb_helper->crtc_info[i].mode_set;
> +			crtc = mode_set->crtc;
> +
> +			/*
> +			 * Only call drm_crtc_wait_one_vblank for crtcs that
> +			 * are currently enabled.
> +			 */
> +			if (!crtc->enabled)
> +				continue;
> +
> +			ret = drm_crtc_vblank_get(crtc);
> +			if (!ret) {
> +				drm_crtc_wait_one_vblank(crtc);
> +				drm_crtc_vblank_put(crtc);
> +			}

This looks quite sub-optimal. It should rather do something along the
lines of what drm_atomic_helper_wait_for_vblanks() does.

> +		}
> +		goto unlock;
> +	default:
> +		ret = -ENOTTY;
> +	}
> +
> +unlock:
> +	drm_modeset_unlock_all(dev);
> +	return ret;
> +}
> +EXPORT_SYMBOL(drm_fb_helper_ioctl);
> +
> +/**
>   * drm_fb_helper_check_var - implementation for ->fb_check_var
>   * @var: screeninfo to check
>   * @info: fbdev registered by the helper
> diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
> index 975deedd593e..460be9d9fa98 100644
> --- a/include/drm/drm_fb_helper.h
> +++ b/include/drm/drm_fb_helper.h
> @@ -230,7 +230,8 @@ struct drm_fb_helper {
>  	.fb_blank	= drm_fb_helper_blank, \
>  	.fb_pan_display	= drm_fb_helper_pan_display, \
>  	.fb_debug_enter = drm_fb_helper_debug_enter, \
> -	.fb_debug_leave = drm_fb_helper_debug_leave
> +	.fb_debug_leave = drm_fb_helper_debug_leave, \
> +	.fb_ioctl	= drm_fb_helper_ioctl
>  
>  #ifdef CONFIG_DRM_FBDEV_EMULATION
>  void drm_fb_helper_prepare(struct drm_device *dev, struct drm_fb_helper *helper,
> @@ -286,6 +287,8 @@ void drm_fb_helper_set_suspend_unlocked(struct drm_fb_helper *fb_helper,
>  
>  int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info);
>  
> +int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg);
> +
>  int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper);
>  int drm_fb_helper_initial_config(struct drm_fb_helper *fb_helper, int bpp_sel);
>  int drm_fb_helper_single_add_all_connectors(struct drm_fb_helper *fb_helper);
> -- 
> git-series 0.8.11
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Ville Syrjälä
Intel OTC
_______________________________________________
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Re: [PATCH v2 2/2] drm/fb_helper: implement ioctl FBIO_WAITFORVSYNC

[Maxime Ripard]

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Hi Ville,

On Fri, Feb 10, 2017 at 04:06:05PM +0200, Ville Syrjälä wrote:
> On Thu, Feb 02, 2017 at 11:31:57AM +0100, Maxime Ripard wrote:
> > From: Stefan Christ <s.christ@phytec.de>
> > 
> > Implement legacy framebuffer ioctl FBIO_WAITFORVSYNC in the generic
> > framebuffer emulation driver. Legacy framebuffer users like non kms/drm
> > based OpenGL(ES)/EGL implementations may require the ioctl to
> > synchronize drawing or buffer flip for double buffering. It is tested on
> > the i.MX6.
> > 
> > Code is based on
> >     https://github.com/Xilinx/linux-xlnx/blob/master/drivers/gpu/drm/xilinx/xilinx_drm_fb.c#L196
> > 
> > Signed-off-by: Stefan Christ <s.christ@phytec.de>
> > Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> > ---
> >  drivers/gpu/drm/drm_fb_helper.c | 55 ++++++++++++++++++++++++++++++++++-
> >  include/drm/drm_fb_helper.h     |  5 ++-
> >  2 files changed, 59 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> > index e934b541feea..39a3532e311c 100644
> > --- a/drivers/gpu/drm/drm_fb_helper.c
> > +++ b/drivers/gpu/drm/drm_fb_helper.c
> > @@ -1234,6 +1234,61 @@ int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
> >  EXPORT_SYMBOL(drm_fb_helper_setcmap);
> >  
> >  /**
> > + * drm_fb_helper_ioctl - legacy ioctl implementation
> > + * @info: fbdev registered by the helper
> > + * @cmd: ioctl command
> > + * @arg: ioctl argument
> > + *
> > + * A helper to implement the standard fbdev ioctl. Only
> > + * FBIO_WAITFORVSYNC is implemented for now.
> > + */
> > +int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg)
> > +{
> > +	struct drm_fb_helper *fb_helper = info->par;
> > +	struct drm_device *dev = fb_helper->dev;
> > +	unsigned int i;
> > +	int ret = 0;
> > +
> > +	drm_modeset_lock_all(dev);
> > +	if (!drm_fb_helper_is_bound(fb_helper)) {
> > +		drm_modeset_unlock_all(dev);
> > +		return -EBUSY;
> > +	}
> > +
> > +	switch (cmd) {
> > +	case FBIO_WAITFORVSYNC:
> > +		for (i = 0; i < fb_helper->crtc_count; i++) {
> 
> FBIO_WAITFORVSYNC takes the crtc as a parmeter, so I'm not sure we want
> to do this for all the crtcs. Though what that crtc means for fb is
> rather poorly defined.

I guess I could just use that index to retrieve only the right CRTC in
fb_helper->crtc_info.

> 
> > +			struct drm_mode_set *mode_set;
> > +			struct drm_crtc *crtc;
> > +
> > +			mode_set = &fb_helper->crtc_info[i].mode_set;
> > +			crtc = mode_set->crtc;
> > +
> > +			/*
> > +			 * Only call drm_crtc_wait_one_vblank for crtcs that
> > +			 * are currently enabled.
> > +			 */
> > +			if (!crtc->enabled)
> > +				continue;
> > +
> > +			ret = drm_crtc_vblank_get(crtc);
> > +			if (!ret) {
> > +				drm_crtc_wait_one_vblank(crtc);
> > +				drm_crtc_vblank_put(crtc);
> > +			}
> 
> This looks quite sub-optimal. It should rather do something along the
> lines of what drm_atomic_helper_wait_for_vblanks() does.

How is that suboptimal?

As far as I can see, they are both doing the same thing (except one
does for all the CRTCs, but I guess that would no longer be needed
with the change you suggested above):
  - drm_crtc_vblank_get
  - Wait for the vblank count to change
  - drm_crtc_vblank_put

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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Re: [PATCH v2 2/2] drm/fb_helper: implement ioctl FBIO_WAITFORVSYNC

[Maxime Ripard]

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Hi Ville,

On Fri, Feb 10, 2017 at 04:06:05PM +0200, Ville Syrjälä wrote:
> On Thu, Feb 02, 2017 at 11:31:57AM +0100, Maxime Ripard wrote:
> > From: Stefan Christ <s.christ@phytec.de>
> > 
> > Implement legacy framebuffer ioctl FBIO_WAITFORVSYNC in the generic
> > framebuffer emulation driver. Legacy framebuffer users like non kms/drm
> > based OpenGL(ES)/EGL implementations may require the ioctl to
> > synchronize drawing or buffer flip for double buffering. It is tested on
> > the i.MX6.
> > 
> > Code is based on
> >     https://github.com/Xilinx/linux-xlnx/blob/master/drivers/gpu/drm/xilinx/xilinx_drm_fb.c#L196
> > 
> > Signed-off-by: Stefan Christ <s.christ@phytec.de>
> > Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> > ---
> >  drivers/gpu/drm/drm_fb_helper.c | 55 ++++++++++++++++++++++++++++++++++-
> >  include/drm/drm_fb_helper.h     |  5 ++-
> >  2 files changed, 59 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> > index e934b541feea..39a3532e311c 100644
> > --- a/drivers/gpu/drm/drm_fb_helper.c
> > +++ b/drivers/gpu/drm/drm_fb_helper.c
> > @@ -1234,6 +1234,61 @@ int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
> >  EXPORT_SYMBOL(drm_fb_helper_setcmap);
> >  
> >  /**
> > + * drm_fb_helper_ioctl - legacy ioctl implementation
> > + * @info: fbdev registered by the helper
> > + * @cmd: ioctl command
> > + * @arg: ioctl argument
> > + *
> > + * A helper to implement the standard fbdev ioctl. Only
> > + * FBIO_WAITFORVSYNC is implemented for now.
> > + */
> > +int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg)
> > +{
> > +	struct drm_fb_helper *fb_helper = info->par;
> > +	struct drm_device *dev = fb_helper->dev;
> > +	unsigned int i;
> > +	int ret = 0;
> > +
> > +	drm_modeset_lock_all(dev);
> > +	if (!drm_fb_helper_is_bound(fb_helper)) {
> > +		drm_modeset_unlock_all(dev);
> > +		return -EBUSY;
> > +	}
> > +
> > +	switch (cmd) {
> > +	case FBIO_WAITFORVSYNC:
> > +		for (i = 0; i < fb_helper->crtc_count; i++) {
> 
> FBIO_WAITFORVSYNC takes the crtc as a parmeter, so I'm not sure we want
> to do this for all the crtcs. Though what that crtc means for fb is
> rather poorly defined.

I guess I could just use that index to retrieve only the right CRTC in
fb_helper->crtc_info.

> 
> > +			struct drm_mode_set *mode_set;
> > +			struct drm_crtc *crtc;
> > +
> > +			mode_set = &fb_helper->crtc_info[i].mode_set;
> > +			crtc = mode_set->crtc;
> > +
> > +			/*
> > +			 * Only call drm_crtc_wait_one_vblank for crtcs that
> > +			 * are currently enabled.
> > +			 */
> > +			if (!crtc->enabled)
> > +				continue;
> > +
> > +			ret = drm_crtc_vblank_get(crtc);
> > +			if (!ret) {
> > +				drm_crtc_wait_one_vblank(crtc);
> > +				drm_crtc_vblank_put(crtc);
> > +			}
> 
> This looks quite sub-optimal. It should rather do something along the
> lines of what drm_atomic_helper_wait_for_vblanks() does.

How is that suboptimal?

As far as I can see, they are both doing the same thing (except one
does for all the CRTCs, but I guess that would no longer be needed
with the change you suggested above):
  - drm_crtc_vblank_get
  - Wait for the vblank count to change
  - drm_crtc_vblank_put

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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Re: [PATCH v2 2/2] drm/fb_helper: implement ioctl FBIO_WAITFORVSYNC

[Ville Syrjälä]

On Mon, Feb 13, 2017 at 11:35:18AM +0100, Maxime Ripard wrote:
> Hi Ville,
> 
> On Fri, Feb 10, 2017 at 04:06:05PM +0200, Ville Syrjälä wrote:
> > On Thu, Feb 02, 2017 at 11:31:57AM +0100, Maxime Ripard wrote:
> > > From: Stefan Christ <s.christ@phytec.de>
> > > 
> > > Implement legacy framebuffer ioctl FBIO_WAITFORVSYNC in the generic
> > > framebuffer emulation driver. Legacy framebuffer users like non kms/drm
> > > based OpenGL(ES)/EGL implementations may require the ioctl to
> > > synchronize drawing or buffer flip for double buffering. It is tested on
> > > the i.MX6.
> > > 
> > > Code is based on
> > >     https://github.com/Xilinx/linux-xlnx/blob/master/drivers/gpu/drm/xilinx/xilinx_drm_fb.c#L196
> > > 
> > > Signed-off-by: Stefan Christ <s.christ@phytec.de>
> > > Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> > > ---
> > >  drivers/gpu/drm/drm_fb_helper.c | 55 ++++++++++++++++++++++++++++++++++-
> > >  include/drm/drm_fb_helper.h     |  5 ++-
> > >  2 files changed, 59 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> > > index e934b541feea..39a3532e311c 100644
> > > --- a/drivers/gpu/drm/drm_fb_helper.c
> > > +++ b/drivers/gpu/drm/drm_fb_helper.c
> > > @@ -1234,6 +1234,61 @@ int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
> > >  EXPORT_SYMBOL(drm_fb_helper_setcmap);
> > >  
> > >  /**
> > > + * drm_fb_helper_ioctl - legacy ioctl implementation
> > > + * @info: fbdev registered by the helper
> > > + * @cmd: ioctl command
> > > + * @arg: ioctl argument
> > > + *
> > > + * A helper to implement the standard fbdev ioctl. Only
> > > + * FBIO_WAITFORVSYNC is implemented for now.
> > > + */
> > > +int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg)
> > > +{
> > > +	struct drm_fb_helper *fb_helper = info->par;
> > > +	struct drm_device *dev = fb_helper->dev;
> > > +	unsigned int i;
> > > +	int ret = 0;
> > > +
> > > +	drm_modeset_lock_all(dev);
> > > +	if (!drm_fb_helper_is_bound(fb_helper)) {
> > > +		drm_modeset_unlock_all(dev);
> > > +		return -EBUSY;
> > > +	}
> > > +
> > > +	switch (cmd) {
> > > +	case FBIO_WAITFORVSYNC:
> > > +		for (i = 0; i < fb_helper->crtc_count; i++) {
> > 
> > FBIO_WAITFORVSYNC takes the crtc as a parmeter, so I'm not sure we want
> > to do this for all the crtcs. Though what that crtc means for fb is
> > rather poorly defined.
> 
> I guess I could just use that index to retrieve only the right CRTC in
> fb_helper->crtc_info.
> 
> > 
> > > +			struct drm_mode_set *mode_set;
> > > +			struct drm_crtc *crtc;
> > > +
> > > +			mode_set = &fb_helper->crtc_info[i].mode_set;
> > > +			crtc = mode_set->crtc;
> > > +
> > > +			/*
> > > +			 * Only call drm_crtc_wait_one_vblank for crtcs that
> > > +			 * are currently enabled.
> > > +			 */
> > > +			if (!crtc->enabled)
> > > +				continue;
> > > +
> > > +			ret = drm_crtc_vblank_get(crtc);
> > > +			if (!ret) {
> > > +				drm_crtc_wait_one_vblank(crtc);
> > > +				drm_crtc_vblank_put(crtc);
> > > +			}
> > 
> > This looks quite sub-optimal. It should rather do something along the
> > lines of what drm_atomic_helper_wait_for_vblanks() does.
> 
> How is that suboptimal?

You're serializing the waits rather than doing them in parallel.

Let's look at a simple three crtc example (|=vblank):

        time -->
CRTC 1:     |     |     |     |
CRTC 2:   |     |     |     |
CRTC 3: |     |     |     |

Your code waits until here:
            |   |   |
            1   2   3
                    ^

Optimal code would wait until here:
            |
            ^
 
-- 
Ville Syrjälä
Intel OTC

Re: [PATCH v2 2/2] drm/fb_helper: implement ioctl FBIO_WAITFORVSYNC

[Ville Syrjälä]

On Mon, Feb 13, 2017 at 11:35:18AM +0100, Maxime Ripard wrote:
> Hi Ville,
> 
> On Fri, Feb 10, 2017 at 04:06:05PM +0200, Ville Syrjälä wrote:
> > On Thu, Feb 02, 2017 at 11:31:57AM +0100, Maxime Ripard wrote:
> > > From: Stefan Christ <s.christ@phytec.de>
> > > 
> > > Implement legacy framebuffer ioctl FBIO_WAITFORVSYNC in the generic
> > > framebuffer emulation driver. Legacy framebuffer users like non kms/drm
> > > based OpenGL(ES)/EGL implementations may require the ioctl to
> > > synchronize drawing or buffer flip for double buffering. It is tested on
> > > the i.MX6.
> > > 
> > > Code is based on
> > >     https://github.com/Xilinx/linux-xlnx/blob/master/drivers/gpu/drm/xilinx/xilinx_drm_fb.c#L196
> > > 
> > > Signed-off-by: Stefan Christ <s.christ@phytec.de>
> > > Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> > > ---
> > >  drivers/gpu/drm/drm_fb_helper.c | 55 ++++++++++++++++++++++++++++++++++-
> > >  include/drm/drm_fb_helper.h     |  5 ++-
> > >  2 files changed, 59 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> > > index e934b541feea..39a3532e311c 100644
> > > --- a/drivers/gpu/drm/drm_fb_helper.c
> > > +++ b/drivers/gpu/drm/drm_fb_helper.c
> > > @@ -1234,6 +1234,61 @@ int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
> > >  EXPORT_SYMBOL(drm_fb_helper_setcmap);
> > >  
> > >  /**
> > > + * drm_fb_helper_ioctl - legacy ioctl implementation
> > > + * @info: fbdev registered by the helper
> > > + * @cmd: ioctl command
> > > + * @arg: ioctl argument
> > > + *
> > > + * A helper to implement the standard fbdev ioctl. Only
> > > + * FBIO_WAITFORVSYNC is implemented for now.
> > > + */
> > > +int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg)
> > > +{
> > > +	struct drm_fb_helper *fb_helper = info->par;
> > > +	struct drm_device *dev = fb_helper->dev;
> > > +	unsigned int i;
> > > +	int ret = 0;
> > > +
> > > +	drm_modeset_lock_all(dev);
> > > +	if (!drm_fb_helper_is_bound(fb_helper)) {
> > > +		drm_modeset_unlock_all(dev);
> > > +		return -EBUSY;
> > > +	}
> > > +
> > > +	switch (cmd) {
> > > +	case FBIO_WAITFORVSYNC:
> > > +		for (i = 0; i < fb_helper->crtc_count; i++) {
> > 
> > FBIO_WAITFORVSYNC takes the crtc as a parmeter, so I'm not sure we want
> > to do this for all the crtcs. Though what that crtc means for fb is
> > rather poorly defined.
> 
> I guess I could just use that index to retrieve only the right CRTC in
> fb_helper->crtc_info.
> 
> > 
> > > +			struct drm_mode_set *mode_set;
> > > +			struct drm_crtc *crtc;
> > > +
> > > +			mode_set = &fb_helper->crtc_info[i].mode_set;
> > > +			crtc = mode_set->crtc;
> > > +
> > > +			/*
> > > +			 * Only call drm_crtc_wait_one_vblank for crtcs that
> > > +			 * are currently enabled.
> > > +			 */
> > > +			if (!crtc->enabled)
> > > +				continue;
> > > +
> > > +			ret = drm_crtc_vblank_get(crtc);
> > > +			if (!ret) {
> > > +				drm_crtc_wait_one_vblank(crtc);
> > > +				drm_crtc_vblank_put(crtc);
> > > +			}
> > 
> > This looks quite sub-optimal. It should rather do something along the
> > lines of what drm_atomic_helper_wait_for_vblanks() does.
> 
> How is that suboptimal?

You're serializing the waits rather than doing them in parallel.

Let's look at a simple three crtc example (|=vblank):

        time -->
CRTC 1:     |     |     |     |
CRTC 2:   |     |     |     |
CRTC 3: |     |     |     |

Your code waits until here:
            |   |   |
            1   2   3
                    ^

Optimal code would wait until here:
            |
            ^
 
-- 
Ville Syrjälä
Intel OTC
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Re: [PATCH v2 2/2] drm/fb_helper: implement ioctl FBIO_WAITFORVSYNC

[Maxime Ripard]

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Hi,

On Mon, Feb 13, 2017 at 04:45:33PM +0200, Ville Syrjälä wrote:
> On Mon, Feb 13, 2017 at 11:35:18AM +0100, Maxime Ripard wrote:
> > Hi Ville,
> > 
> > On Fri, Feb 10, 2017 at 04:06:05PM +0200, Ville Syrjälä wrote:
> > > On Thu, Feb 02, 2017 at 11:31:57AM +0100, Maxime Ripard wrote:
> > > > From: Stefan Christ <s.christ@phytec.de>
> > > > 
> > > > Implement legacy framebuffer ioctl FBIO_WAITFORVSYNC in the generic
> > > > framebuffer emulation driver. Legacy framebuffer users like non kms/drm
> > > > based OpenGL(ES)/EGL implementations may require the ioctl to
> > > > synchronize drawing or buffer flip for double buffering. It is tested on
> > > > the i.MX6.
> > > > 
> > > > Code is based on
> > > >     https://github.com/Xilinx/linux-xlnx/blob/master/drivers/gpu/drm/xilinx/xilinx_drm_fb.c#L196
> > > > 
> > > > Signed-off-by: Stefan Christ <s.christ@phytec.de>
> > > > Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> > > > ---
> > > >  drivers/gpu/drm/drm_fb_helper.c | 55 ++++++++++++++++++++++++++++++++++-
> > > >  include/drm/drm_fb_helper.h     |  5 ++-
> > > >  2 files changed, 59 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> > > > index e934b541feea..39a3532e311c 100644
> > > > --- a/drivers/gpu/drm/drm_fb_helper.c
> > > > +++ b/drivers/gpu/drm/drm_fb_helper.c
> > > > @@ -1234,6 +1234,61 @@ int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
> > > >  EXPORT_SYMBOL(drm_fb_helper_setcmap);
> > > >  
> > > >  /**
> > > > + * drm_fb_helper_ioctl - legacy ioctl implementation
> > > > + * @info: fbdev registered by the helper
> > > > + * @cmd: ioctl command
> > > > + * @arg: ioctl argument
> > > > + *
> > > > + * A helper to implement the standard fbdev ioctl. Only
> > > > + * FBIO_WAITFORVSYNC is implemented for now.
> > > > + */
> > > > +int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg)
> > > > +{
> > > > +	struct drm_fb_helper *fb_helper = info->par;
> > > > +	struct drm_device *dev = fb_helper->dev;
> > > > +	unsigned int i;
> > > > +	int ret = 0;
> > > > +
> > > > +	drm_modeset_lock_all(dev);
> > > > +	if (!drm_fb_helper_is_bound(fb_helper)) {
> > > > +		drm_modeset_unlock_all(dev);
> > > > +		return -EBUSY;
> > > > +	}
> > > > +
> > > > +	switch (cmd) {
> > > > +	case FBIO_WAITFORVSYNC:
> > > > +		for (i = 0; i < fb_helper->crtc_count; i++) {
> > > 
> > > FBIO_WAITFORVSYNC takes the crtc as a parmeter, so I'm not sure we want
> > > to do this for all the crtcs. Though what that crtc means for fb is
> > > rather poorly defined.
> > 
> > I guess I could just use that index to retrieve only the right CRTC in
> > fb_helper->crtc_info.
> > 
> > > 
> > > > +			struct drm_mode_set *mode_set;
> > > > +			struct drm_crtc *crtc;
> > > > +
> > > > +			mode_set = &fb_helper->crtc_info[i].mode_set;
> > > > +			crtc = mode_set->crtc;
> > > > +
> > > > +			/*
> > > > +			 * Only call drm_crtc_wait_one_vblank for crtcs that
> > > > +			 * are currently enabled.
> > > > +			 */
> > > > +			if (!crtc->enabled)
> > > > +				continue;
> > > > +
> > > > +			ret = drm_crtc_vblank_get(crtc);
> > > > +			if (!ret) {
> > > > +				drm_crtc_wait_one_vblank(crtc);
> > > > +				drm_crtc_vblank_put(crtc);
> > > > +			}
> > > 
> > > This looks quite sub-optimal. It should rather do something along the
> > > lines of what drm_atomic_helper_wait_for_vblanks() does.
> > 
> > How is that suboptimal?
> 
> You're serializing the waits rather than doing them in parallel.
> 
> Let's look at a simple three crtc example (|=vblank):
> 
>         time -->
> CRTC 1:     |     |     |     |
> CRTC 2:   |     |     |     |
> CRTC 3: |     |     |     |
> 
> Your code waits until here:
>             |   |   |
>             1   2   3
>                     ^
> 
> Optimal code would wait until here:
>             |
>             ^

Ah, right. But then, this would happen only if we loop over all the
CRTCs, which shouldn't happen in the v2 as you suggested.

Out of curiosity, how could we fix this if we were to loop over all
the framebuffers? By waiting on any vblank count to change?

Thanks,
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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Re: [PATCH v2 2/2] drm/fb_helper: implement ioctl FBIO_WAITFORVSYNC

[Maxime Ripard]

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Hi,

On Mon, Feb 13, 2017 at 04:45:33PM +0200, Ville Syrjälä wrote:
> On Mon, Feb 13, 2017 at 11:35:18AM +0100, Maxime Ripard wrote:
> > Hi Ville,
> > 
> > On Fri, Feb 10, 2017 at 04:06:05PM +0200, Ville Syrjälä wrote:
> > > On Thu, Feb 02, 2017 at 11:31:57AM +0100, Maxime Ripard wrote:
> > > > From: Stefan Christ <s.christ@phytec.de>
> > > > 
> > > > Implement legacy framebuffer ioctl FBIO_WAITFORVSYNC in the generic
> > > > framebuffer emulation driver. Legacy framebuffer users like non kms/drm
> > > > based OpenGL(ES)/EGL implementations may require the ioctl to
> > > > synchronize drawing or buffer flip for double buffering. It is tested on
> > > > the i.MX6.
> > > > 
> > > > Code is based on
> > > >     https://github.com/Xilinx/linux-xlnx/blob/master/drivers/gpu/drm/xilinx/xilinx_drm_fb.c#L196
> > > > 
> > > > Signed-off-by: Stefan Christ <s.christ@phytec.de>
> > > > Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> > > > ---
> > > >  drivers/gpu/drm/drm_fb_helper.c | 55 ++++++++++++++++++++++++++++++++++-
> > > >  include/drm/drm_fb_helper.h     |  5 ++-
> > > >  2 files changed, 59 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> > > > index e934b541feea..39a3532e311c 100644
> > > > --- a/drivers/gpu/drm/drm_fb_helper.c
> > > > +++ b/drivers/gpu/drm/drm_fb_helper.c
> > > > @@ -1234,6 +1234,61 @@ int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
> > > >  EXPORT_SYMBOL(drm_fb_helper_setcmap);
> > > >  
> > > >  /**
> > > > + * drm_fb_helper_ioctl - legacy ioctl implementation
> > > > + * @info: fbdev registered by the helper
> > > > + * @cmd: ioctl command
> > > > + * @arg: ioctl argument
> > > > + *
> > > > + * A helper to implement the standard fbdev ioctl. Only
> > > > + * FBIO_WAITFORVSYNC is implemented for now.
> > > > + */
> > > > +int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg)
> > > > +{
> > > > +	struct drm_fb_helper *fb_helper = info->par;
> > > > +	struct drm_device *dev = fb_helper->dev;
> > > > +	unsigned int i;
> > > > +	int ret = 0;
> > > > +
> > > > +	drm_modeset_lock_all(dev);
> > > > +	if (!drm_fb_helper_is_bound(fb_helper)) {
> > > > +		drm_modeset_unlock_all(dev);
> > > > +		return -EBUSY;
> > > > +	}
> > > > +
> > > > +	switch (cmd) {
> > > > +	case FBIO_WAITFORVSYNC:
> > > > +		for (i = 0; i < fb_helper->crtc_count; i++) {
> > > 
> > > FBIO_WAITFORVSYNC takes the crtc as a parmeter, so I'm not sure we want
> > > to do this for all the crtcs. Though what that crtc means for fb is
> > > rather poorly defined.
> > 
> > I guess I could just use that index to retrieve only the right CRTC in
> > fb_helper->crtc_info.
> > 
> > > 
> > > > +			struct drm_mode_set *mode_set;
> > > > +			struct drm_crtc *crtc;
> > > > +
> > > > +			mode_set = &fb_helper->crtc_info[i].mode_set;
> > > > +			crtc = mode_set->crtc;
> > > > +
> > > > +			/*
> > > > +			 * Only call drm_crtc_wait_one_vblank for crtcs that
> > > > +			 * are currently enabled.
> > > > +			 */
> > > > +			if (!crtc->enabled)
> > > > +				continue;
> > > > +
> > > > +			ret = drm_crtc_vblank_get(crtc);
> > > > +			if (!ret) {
> > > > +				drm_crtc_wait_one_vblank(crtc);
> > > > +				drm_crtc_vblank_put(crtc);
> > > > +			}
> > > 
> > > This looks quite sub-optimal. It should rather do something along the
> > > lines of what drm_atomic_helper_wait_for_vblanks() does.
> > 
> > How is that suboptimal?
> 
> You're serializing the waits rather than doing them in parallel.
> 
> Let's look at a simple three crtc example (|=vblank):
> 
>         time -->
> CRTC 1:     |     |     |     |
> CRTC 2:   |     |     |     |
> CRTC 3: |     |     |     |
> 
> Your code waits until here:
>             |   |   |
>             1   2   3
>                     ^
> 
> Optimal code would wait until here:
>             |
>             ^

Ah, right. But then, this would happen only if we loop over all the
CRTCs, which shouldn't happen in the v2 as you suggested.

Out of curiosity, how could we fix this if we were to loop over all
the framebuffers? By waiting on any vblank count to change?

Thanks,
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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