[PATCH RFC 3/6] drm/mediatek: ovl: Fix misaligned layer source size on AFBC mode

[Nícolas F. R. A. Prado]

On Mon, 2026-02-02 at 08:46 +0000, CK Hu (胡俊光) wrote:
> On Tue, 2025-12-30 at 11:03 -0300, Nícolas F. R. A. Prado wrote:
> > From: Ariel D'Alessandro <ariel.dalessandro at collabora.com>
> > 
> > In AFBC mode, OVL_SRC_SIZE must be block aligned. Due to this
> > limitation
> > of the AFBC format, OVL_CLIP needs to be used to achieve the
> > desired
> > output size of the layer while still meeting the alignment
> > constraints.
> > Failure to do this will result in vblank timeouts and no rendered
> > output
> > when the AFBC data source isn't aligned to the AFBC block (32x8).
> > 
> > Configure OVL_CLIP so unaligned AFBC layers can be displayed.
> > 
> > The following illustrates how the alignment is achieved through the
> > clip
> > settings for the horizontal coordinates, the vertical coordinates
> > are
> > analogous:
> > 
> > /------------------------------------------------\
> > >                                                |
> > >            ........................            |
> > >            ........................            |
> > >            ........................            |
> > >            ........................            |
> > >                                                |
> > \------------------------------------------------/
> >      |       |                      |       |
> >      |       src.x1                 src.x2  |
> >      |       |                      |       |
> >      |       |<-------------------->|       |
> >      |              src_width               |
> 
> This patch looks to me.
> But "In AFBC mode, OVL_SRC_SIZE must be block aligned", so this graph
> should show as:
> 
>      |       src.x1                 src.x2  |
>      |       |                      |       |
>      |       |                      |       |
>      N * AFBC_DATA_BLOCK_WIDTH      |       M * AFBC_DATA_BLOCK_WIDTH
>      |       |                      |       |
>      |<----->|                      |<----->|
>      |clip_left                      clip_right
>      |                                      |
>      |<------------------------------------>|
>      |              src_width               |

Ah yes indeed, thanks for spotting that!

-- 
Thanks,

Nícolas