[PATCH] drm: Check actual format for legacy pageflip.

[Daniel Vetter]

On Sat, Jan 02, 2021 at 04:31:36PM +0100, Mario Kleiner wrote:
> On Sat, Jan 2, 2021 at 3:02 PM Bas Nieuwenhuizen
> <bas at basnieuwenhuizen.nl> wrote:
> >
> > With modifiers one can actually have different format_info structs
> > for the same format, which now matters for AMDGPU since we convert
> > implicit modifiers to explicit modifiers with multiple planes.
> >
> > I checked other drivers and it doesn't look like they end up triggering
> > this case so I think this is safe to relax.
> >
> > Signed-off-by: Bas Nieuwenhuizen <bas at basnieuwenhuizen.nl>
> > Fixes: 816853f9dc40 ("drm/amd/display: Set new format info for converted metadata.")
> > ---
> >  drivers/gpu/drm/drm_plane.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
> > index e6231947f987..f5085990cfac 100644
> > --- a/drivers/gpu/drm/drm_plane.c
> > +++ b/drivers/gpu/drm/drm_plane.c
> > @@ -1163,7 +1163,7 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
> >         if (ret)
> >                 goto out;
> >
> > -       if (old_fb->format != fb->format) {
> > +       if (old_fb->format->format != fb->format->format) {
> 
> This was btw. the original way before Ville made it more strict about
> 4 years ago, to catch issues related to tiling, and more complex
> layouts, like the dcc tiling/retiling introduced by your modifier
> patches. That's why I hope my alternative patch is a good solution for
> atomic drivers while keeping the strictness for potential legacy
> drivers.

Yeah this doesn't work in full generality, because hw might need to do a
full modeset to do a full modeset to reallocate resources (like scanout
fifo space) if the format changes.

But for atomic drivers that should be caught in ->atomic_check, which
should result in -EINVAL, so should do the right thing. So it should be
all good, but imo needs a comment to explain what's going on:

	/*
	 * Only check the FOURCC format code, excluding modifiers. This is
	 * enough for all legacy drivers. Atomic drivers have their own
	 * checks in their ->atomic_check implementation, which will
	 * return -EINVAL if any hw or driver constraint is violated due
	 * to modifier changes.
	 */

Also can you pls cc: intel-gfx to get this vetted by the intel-gfx ci?

With that:

Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

> 
> -mario
> 
> >                 DRM_DEBUG_KMS("Page flip is not allowed to change frame buffer format.\n");
> >                 ret = -EINVAL;
> >                 goto out;
> > --
> > 2.29.2
> >

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