[PATCH] drm/exynos/fbdev: set smem_len for fbdev

[PATCH] drm/exynos/fbdev: set smem_len for fbdev

[Daniel Kurtz]

Commit [0] stopped setting fix.smem_start and fix.smem_len when creating
the fbdev.

[0] 2f1eab8d8ab59e799f7d51d62410b398607a7bc3
  drm/exynos/fbdev: don't set fix.smem/mmio_{start,len}

However, smem_len is used by some userland applications to calculate the
size for mmap.  In particular, it is used by xf86-video-fbdev:

http://cgit.freedesktop.org/xorg/xserver/tree/hw/xfree86/fbdevhw/fbdevhw.c?id=xorg-server-1.15.99.903#n571

So, let's restore setting the smem_len to unbreak things for these users.

Note: we are still leaving smem_start set to 0.

Reported-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
Reported-by: Günther Noack <me@guenthernoack.de>
Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
---
I am able to compile test this change, but would appreciate help testing it
on a system that uses xf86-video-fbdev.

Thanks!

 drivers/gpu/drm/exynos/exynos_drm_fbdev.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/exynos/exynos_drm_fbdev.c b/drivers/gpu/drm/exynos/exynos_drm_fbdev.c
index 5a7cd8b..f865736 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_fbdev.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_fbdev.c
@@ -125,6 +125,7 @@ static int exynos_drm_fbdev_update(struct drm_fb_helper *helper,
 
 	fbi->screen_base = buffer->kvaddr;
 	fbi->screen_size = size;
+	fbi->fix.smem_len = size;
 
 	return 0;
 }
-- 
2.1.0.rc2.206.gedb03e5

Re: [PATCH] drm/exynos/fbdev: set smem_len for fbdev

[Günther Noack]

This patch works on my hardware.  Xorg starts up fine with fbdev now.
Thanks for the fix!

--Günther

Daniel Kurtz <djkurtz@chromium.org> writes:

> Commit [0] stopped setting fix.smem_start and fix.smem_len when creating
> the fbdev.
>
> [0] 2f1eab8d8ab59e799f7d51d62410b398607a7bc3
>   drm/exynos/fbdev: don't set fix.smem/mmio_{start,len}
>
> However, smem_len is used by some userland applications to calculate the
> size for mmap.  In particular, it is used by xf86-video-fbdev:
>
> http://cgit.freedesktop.org/xorg/xserver/tree/hw/xfree86/fbdevhw/fbdevhw.c?id=xorg-server-1.15.99.903#n571
>
> So, let's restore setting the smem_len to unbreak things for these users.
>
> Note: we are still leaving smem_start set to 0.
>
> Reported-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
> Reported-by: Günther Noack <me@guenthernoack.de>
> Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
> ---
> I am able to compile test this change, but would appreciate help testing it
> on a system that uses xf86-video-fbdev.
>
> Thanks!
>
>  drivers/gpu/drm/exynos/exynos_drm_fbdev.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/gpu/drm/exynos/exynos_drm_fbdev.c b/drivers/gpu/drm/exynos/exynos_drm_fbdev.c
> index 5a7cd8b..f865736 100644
> --- a/drivers/gpu/drm/exynos/exynos_drm_fbdev.c
> +++ b/drivers/gpu/drm/exynos/exynos_drm_fbdev.c
> @@ -125,6 +125,7 @@ static int exynos_drm_fbdev_update(struct drm_fb_helper *helper,
>  
>  	fbi->screen_base = buffer->kvaddr;
>  	fbi->screen_size = size;
> +	fbi->fix.smem_len = size;
>  
>  	return 0;
>  }
> -- 
> 2.1.0.rc2.206.gedb03e5

Re: [PATCH] drm/exynos/fbdev: set smem_len for fbdev

[Geert Uytterhoeven]

On Sun, Aug 24, 2014 at 4:50 PM, Daniel Kurtz <djkurtz@chromium.org> wrote:
> Commit [0] stopped setting fix.smem_start and fix.smem_len when creating
> the fbdev.
>
> [0] 2f1eab8d8ab59e799f7d51d62410b398607a7bc3
>   drm/exynos/fbdev: don't set fix.smem/mmio_{start,len}
>
> However, smem_len is used by some userland applications to calculate the
> size for mmap.  In particular, it is used by xf86-video-fbdev:
>
> http://cgit.freedesktop.org/xorg/xserver/tree/hw/xfree86/fbdevhw/fbdevhw.c?id=xorg-server-1.15.99.903#n571
>
> So, let's restore setting the smem_len to unbreak things for these users.
>
> Note: we are still leaving smem_start set to 0.

Doesn't this cause a system crash when userspace (e.g. fbtest) writes into
the mmap()ed /dev/fb*, as the wrong MMIO region is mapped?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH] drm/exynos/fbdev: set smem_len for fbdev

[Daniel Kurtz]

On Thu, Sep 25, 2014 at 5:32 PM, Geert Uytterhoeven
<geert@linux-m68k.org> wrote:
> On Sun, Aug 24, 2014 at 4:50 PM, Daniel Kurtz <djkurtz@chromium.org> wrote:
>> Commit [0] stopped setting fix.smem_start and fix.smem_len when creating
>> the fbdev.
>>
>> [0] 2f1eab8d8ab59e799f7d51d62410b398607a7bc3
>>   drm/exynos/fbdev: don't set fix.smem/mmio_{start,len}
>>
>> However, smem_len is used by some userland applications to calculate the
>> size for mmap.  In particular, it is used by xf86-video-fbdev:
>>
>> http://cgit.freedesktop.org/xorg/xserver/tree/hw/xfree86/fbdevhw/fbdevhw.c?id=xorg-server-1.15.99.903#n571
>>
>> So, let's restore setting the smem_len to unbreak things for these users.
>>
>> Note: we are still leaving smem_start set to 0.
>
> Doesn't this cause a system crash when userspace (e.g. fbtest) writes into
> the mmap()ed /dev/fb*, as the wrong MMIO region is mapped?

Do you see a crash during testing, or is your question hypothetical?

I don't think there will be one.  exynos's fbev defines its own
fb_ops.fb_mmap, which uses dma_mmap_attrs() to mmap the fb's gem
buffer, which was allocated by dma_alloc_attrs().  This bypasses the
code in drivers/video/fbmem.c:fb_mmap() that references
fix.smem_start.

But, perhaps I am missing something?

-Dan

>
> Gr{oetje,eeting}s,
>
>                         Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds

Re: [PATCH] drm/exynos/fbdev: set smem_len for fbdev

[Geert Uytterhoeven]

On Thu, Sep 25, 2014 at 12:07 PM, Daniel Kurtz <djkurtz@chromium.org> wrote:
> On Thu, Sep 25, 2014 at 5:32 PM, Geert Uytterhoeven
> <geert@linux-m68k.org> wrote:
>> On Sun, Aug 24, 2014 at 4:50 PM, Daniel Kurtz <djkurtz@chromium.org> wrote:
>>> Commit [0] stopped setting fix.smem_start and fix.smem_len when creating
>>> the fbdev.
>>>
>>> [0] 2f1eab8d8ab59e799f7d51d62410b398607a7bc3
>>>   drm/exynos/fbdev: don't set fix.smem/mmio_{start,len}
>>>
>>> However, smem_len is used by some userland applications to calculate the
>>> size for mmap.  In particular, it is used by xf86-video-fbdev:
>>>
>>> http://cgit.freedesktop.org/xorg/xserver/tree/hw/xfree86/fbdevhw/fbdevhw.c?id=xorg-server-1.15.99.903#n571
>>>
>>> So, let's restore setting the smem_len to unbreak things for these users.
>>>
>>> Note: we are still leaving smem_start set to 0.
>>
>> Doesn't this cause a system crash when userspace (e.g. fbtest) writes into
>> the mmap()ed /dev/fb*, as the wrong MMIO region is mapped?
>
> Do you see a crash during testing, or is your question hypothetical?

It was hypothetical.

> I don't think there will be one.  exynos's fbev defines its own
> fb_ops.fb_mmap, which uses dma_mmap_attrs() to mmap the fb's gem
> buffer, which was allocated by dma_alloc_attrs().  This bypasses the
> code in drivers/video/fbmem.c:fb_mmap() that references
> fix.smem_start.
>
> But, perhaps I am missing something?

Thanks, having your own mapping function explains the lack of crashes.

Still, some weird software may map /dev/mem instead of /dev/fb0, and
use fb_fix.smem_start. But that's also unsafe in the context of LPAE.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds