Re: [PATCH] drm/gem: Check for valid formats

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Apr 12, 2023 at 11:29:23AM -0300, Maíra Canal wrote:
> Currently, drm_gem_fb_create() doesn't check if the pixel format is
> supported, which can lead to the acceptance of invalid pixel formats
> e.g. the acceptance of invalid modifiers. Therefore, add a check for
> valid formats on drm_gem_fb_create().
> 
> Moreover, note that this check is only valid for atomic drivers,
> because, for non-atomic drivers, checking drm_any_plane_has_format() is
> not possible since the format list for the primary plane is fake, and
> we'd therefor reject valid formats.
> 
> Adding this check to drm_gem_fb_create() will guarantee that the
> igt@kms_addfb_basic@addfb25-bad-modifier IGT test passes for drivers
> using this callback.
> 
> Signed-off-by: Maíra Canal <mcanal@igalia.com>

Seems sane enough, assuming all the drivers using this are happy
with the baked in !modifiers -> linear assumption. That might be
a good thing to highlight in the docs.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

BTW long ago I tried to make igt check this stugg a bit
more vehemently:
https://patchwork.freedesktop.org/patch/239814/?series=46876&rev=1
Someone might want to pick that up again and see if it
cab be makde to work with more drivers than just i915.

> ---
> 
> This patch is a recapture of a series I sent a while ago. Initially, I sent a
> patch [1] similar to this one in which I introduced the format check to
> drm_gem_fb_create().
> 
> Based on the feedback on the patch, I placed the check inside
> framebuffer_check() [2] so that it wouldn't be needed to hit any driver-specific
> code path when the check fails. Therefore, we could remove the check from the
> specific drivers (i915, amdgpu, and vmwgfx).
> 
> But, with some new feedback, it was shown that introducing this check inside
> framebuffer_check() is problematic for the i915 driver [3]. So, I kept the check
> inside the i915 driver and removed the check from amdgpu and vmwgfx [4]. But,
> this yet hasn't solved the i915 problem [5].
> 
> As we cannot add the check inside framebuffer_check() without affecting the i915
> behavior, I propose going back to the original patch. This way we can guarantee
> a more uniform behavior from the drivers that use the drm_gem_fb_create()
> callback.
> 
> [1] https://lore.kernel.org/dri-devel/20230103125322.855089-1-mcanal@igalia.com/T/
> [2] https://lore.kernel.org/dri-devel/20230109105807.18172-1-mcanal@igalia.com/T/
> [3] https://lore.kernel.org/dri-devel/Y8AAdW2y7zN7DCUZ@intel.com/
> [4] https://lore.kernel.org/dri-devel/20230113112743.188486-1-mcanal@igalia.com/T/
> [5] https://lore.kernel.org/dri-devel/Y8FXWvEhO7GCRKVJ@intel.com/
> 
> Best Regards,
> - Maíra Canal
> 
> ---
>  Documentation/gpu/todo.rst                   | 7 ++-----
>  drivers/gpu/drm/drm_gem_framebuffer_helper.c | 9 +++++++++
>  2 files changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/gpu/todo.rst b/Documentation/gpu/todo.rst
> index 1f8a5ebe188e..68bdafa0284f 100644
> --- a/Documentation/gpu/todo.rst
> +++ b/Documentation/gpu/todo.rst
> @@ -276,11 +276,8 @@ Various hold-ups:
>  - Need to switch to drm_fbdev_generic_setup(), otherwise a lot of the custom fb
>    setup code can't be deleted.
>  
> -- Many drivers wrap drm_gem_fb_create() only to check for valid formats. For
> -  atomic drivers we could check for valid formats by calling
> -  drm_plane_check_pixel_format() against all planes, and pass if any plane
> -  supports the format. For non-atomic that's not possible since like the format
> -  list for the primary plane is fake and we'd therefor reject valid formats.
> +- Need to switch to drm_gem_fb_create(), as now drm_gem_fb_create() checks for
> +  valid formats for atomic drivers.
>  
>  - Many drivers subclass drm_framebuffer, we'd need a embedding compatible
>    version of the varios drm_gem_fb_create functions. Maybe called
> diff --git a/drivers/gpu/drm/drm_gem_framebuffer_helper.c b/drivers/gpu/drm/drm_gem_framebuffer_helper.c
> index e93533b86037..b8a615a138cd 100644
> --- a/drivers/gpu/drm/drm_gem_framebuffer_helper.c
> +++ b/drivers/gpu/drm/drm_gem_framebuffer_helper.c
> @@ -9,6 +9,7 @@
>  #include <linux/module.h>
>  
>  #include <drm/drm_damage_helper.h>
> +#include <drm/drm_drv.h>
>  #include <drm/drm_fourcc.h>
>  #include <drm/drm_framebuffer.h>
>  #include <drm/drm_gem.h>
> @@ -164,6 +165,14 @@ int drm_gem_fb_init_with_funcs(struct drm_device *dev,
>  		return -EINVAL;
>  	}
>  
> +	if (drm_drv_uses_atomic_modeset(dev) &&
> +	    !drm_any_plane_has_format(dev, mode_cmd->pixel_format,
> +				      mode_cmd->modifier[0])) {
> +		drm_dbg(dev, "Unsupported pixel format %p4cc / modifier 0x%llx\n",
> +			&mode_cmd->pixel_format, mode_cmd->modifier[0]);
> +		return -EINVAL;
> +	}
> +
>  	for (i = 0; i < info->num_planes; i++) {
>  		unsigned int width = mode_cmd->width / (i ? info->hsub : 1);
>  		unsigned int height = mode_cmd->height / (i ? info->vsub : 1);
> -- 
> 2.39.2

-- 
Ville Syrjälä
Intel