Re: [RFC 4/8] drm/fence: add in-fences support

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Apr 14, 2016 at 06:29:37PM -0700, Gustavo Padovan wrote:
> From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> 
> There is now a new property called FENCE_FD attached to every plane
> state that receives the sync_file fd from userspace via the atomic commit
> IOCTL.
> 
> The fd is then translated to a fence (that may be a fence_collection
> subclass or just a normal fence) and then used by DRM to fence_wait() for
> all fences in the sync_file to signal. So it only commits when all
> framebuffers are ready to scanout.
> 
> Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> ---
>  drivers/gpu/drm/Kconfig             | 1 +
>  drivers/gpu/drm/drm_atomic.c        | 8 ++++++++
>  drivers/gpu/drm/drm_atomic_helper.c | 5 +++++
>  drivers/gpu/drm/drm_crtc.c          | 7 +++++++
>  include/drm/drm_crtc.h              | 1 +
>  5 files changed, 22 insertions(+)
> 
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index f2a74d0..3c987e3 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -12,6 +12,7 @@ menuconfig DRM
>  	select I2C
>  	select I2C_ALGOBIT
>  	select DMA_SHARED_BUFFER
> +	select SYNC_FILE
>  	help
>  	  Kernel-level support for the Direct Rendering Infrastructure (DRI)
>  	  introduced in XFree86 4.0. If you say Y here, you need to select
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index 8ee1db8..6702502 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -30,6 +30,7 @@
>  #include <drm/drm_atomic.h>
>  #include <drm/drm_mode.h>
>  #include <drm/drm_plane_helper.h>
> +#include <linux/sync_file.h>
>  
>  /**
>   * drm_atomic_state_default_release -
> @@ -680,6 +681,11 @@ int drm_atomic_plane_set_property(struct drm_plane *plane,
>  		drm_atomic_set_fb_for_plane(state, fb);
>  		if (fb)
>  			drm_framebuffer_unreference(fb);
> +	} else if (property == config->prop_fence_fd) {
> +		state->fence = sync_file_fences_get(val);
> +		if (!state->fence)
> +			return -EINVAL;
> +		fence_get(state->fence);

Yeah, this fence_get must be part of sync_file_fences_get, this code here
has a race (exercise for the reader to describe where things go wrong
here). Also, you need to explicitly filter out -1 here first I think.

Needs an atomic testcase to make sure setting FENCE_FD to -1 doesn't fall
over (since generic userspace might do this in an attempt to restore all
the state).

>  	} else if (property == config->prop_crtc_id) {
>  		struct drm_crtc *crtc = drm_crtc_find(dev, val);
>  		return drm_atomic_set_crtc_for_plane(state, crtc);
> @@ -737,6 +743,8 @@ drm_atomic_plane_get_property(struct drm_plane *plane,
>  
>  	if (property == config->prop_fb_id) {
>  		*val = (state->fb) ? state->fb->base.id : 0;
> +	} else if (property == config->prop_fence_fd) {
> +		*val = -1;
>  	} else if (property == config->prop_crtc_id) {
>  		*val = (state->crtc) ? state->crtc->base.id : 0;
>  	} else if (property == config->prop_crtc_x) {
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index f85ef8c..6ed8339 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -2687,6 +2687,11 @@ void __drm_atomic_helper_plane_destroy_state(struct drm_plane *plane,
>  {
>  	if (state->fb)
>  		drm_framebuffer_unreference(state->fb);
> +
> +	if (state->fence) {
> +		fence_put(state->fence);
> +		state->fence = NULL;

No need to set to NULL, we don't do that for ->fb either.

> +	}
>  }
>  EXPORT_SYMBOL(__drm_atomic_helper_plane_destroy_state);
>  
> diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> index 55ffde5..65212ce 100644
> --- a/drivers/gpu/drm/drm_crtc.c
> +++ b/drivers/gpu/drm/drm_crtc.c
> @@ -1278,6 +1278,7 @@ int drm_universal_plane_init(struct drm_device *dev, struct drm_plane *plane,
>  
>  	if (drm_core_check_feature(dev, DRIVER_ATOMIC)) {
>  		drm_object_attach_property(&plane->base, config->prop_fb_id, 0);
> +		drm_object_attach_property(&plane->base, config->prop_fence_fd, -1);
>  		drm_object_attach_property(&plane->base, config->prop_crtc_id, 0);
>  		drm_object_attach_property(&plane->base, config->prop_crtc_x, 0);
>  		drm_object_attach_property(&plane->base, config->prop_crtc_y, 0);
> @@ -1533,6 +1534,12 @@ static int drm_mode_create_standard_properties(struct drm_device *dev)
>  		return -ENOMEM;
>  	dev->mode_config.prop_fb_id = prop;
>  
> +	prop = drm_property_create_signed_range(dev, DRM_MODE_PROP_ATOMIC,
> +			"FENCE_FD", -1, INT_MAX);
> +	if (!prop)
> +		return -ENOMEM;
> +	dev->mode_config.prop_fence_fd = prop;
> +
>  	prop = drm_property_create_object(dev, DRM_MODE_PROP_ATOMIC,
>  			"CRTC_ID", DRM_MODE_OBJECT_CRTC);
>  	if (!prop)
> diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
> index 8cb377c..5ba3cda 100644
> --- a/include/drm/drm_crtc.h
> +++ b/include/drm/drm_crtc.h
> @@ -2122,6 +2122,7 @@ struct drm_mode_config {
>  	struct drm_property *prop_crtc_w;
>  	struct drm_property *prop_crtc_h;
>  	struct drm_property *prop_fb_id;
> +	struct drm_property *prop_fence_fd;
>  	struct drm_property *prop_crtc_id;
>  	struct drm_property *prop_active;
>  	struct drm_property *prop_mode_id;
> -- 
> 2.5.5
> 

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