[PATCH] drm/amdgpu: Ensure that the modifier requested is supported by plane.

[Bas Nieuwenhuizen]

On Wed, Mar 24, 2021 at 11:13 AM Michel Dänzer <michel at daenzer.net> wrote:

> On 2021-03-23 4:32 p.m., Mark Yacoub wrote:
> > On Tue, Mar 23, 2021 at 11:02 AM Alex Deucher <alexdeucher at gmail.com>
> wrote:
> >>
> >> On Wed, Mar 10, 2021 at 11:15 AM Mark Yacoub <markyacoub at chromium.org>
> wrote:
> >>>
> >>> From: Mark Yacoub <markyacoub at google.com>
> >>>
> >>> On initializing the framebuffer, call drm_any_plane_has_format to do a
> >>> check if the modifier is supported. drm_any_plane_has_format calls
> >>> dm_plane_format_mod_supported which is extended to validate that the
> >>> modifier is on the list of the plane's supported modifiers.
> >>>
> >>> The bug was caught using igt-gpu-tools test:
> kms_addfb_basic.addfb25-bad-modifier
> >>>
> >>> Tested on ChromeOS Zork by turning on the display, running an overlay
> >>> test, and running a YT video.
> >>>
> >>> Cc: Alex Deucher <alexander.deucher at amd.com>
> >>> Cc: Bas Nieuwenhuizen <bas at basnieuwenhuizen.nl>
> >>> Signed-off-by: default avatarMark Yacoub <markyacoub at chromium.org>
> >>
> >> I'm not an expert with modifiers yet.  Will this break chips which
> >> don't currently support modifiers?
> > No it shouldn't. When you don't support modifiers yet, your will
> > default to Linear Modifier (DRM_FORMAT_MOD_LINEAR),
> > [...]
> No modifier support does not imply linear. It's generally signalled via
> DRM_FORMAT_MOD_INVALID, which roughly means "tiling is determined by driver
> specific mechanisms".
>

Doesn't quite work that way in the kernel sadly. If you don't set
DRM_MODE_FB_MODIFIERS then the modifier fields have to be 0 (which happens
to alias DRM_FORMAT_MOD_LINEAR and then now deprecated
DRM_FORMAT_MOD_NONE). This is verified in shared drm code.

(and all userspace code I've seen simply doesn't set DRM_MODE_FB_MODIFIERS
if the incoming modifier is DRM_FORMAT_MOD_INVALID)

>
>
> --
> Earthling Michel Dänzer               |               https://redhat.com
> Libre software enthusiast             |             Mesa and X developer
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