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

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Message-ID: <02b19b310070df99e13aac97f1034299fa9652a2.camel@collabora.com>
Date: Thu, 05 Feb 2026 13:46:12 -0500
From: Nícolas "F. R. A. Prado" <nfraprado@...labora.com>
To: CK Hu (胡俊光)
 <ck.hu@...iatek.com>,  "chunkuang.hu@...nel.org"	
 <chunkuang.hu@...nel.org>, "simona@...ll.ch" <simona@...ll.ch>, 
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 "airlied@...il.com" <airlied@...il.com>,  "greenjustin@...omium.org"	
 <greenjustin@...omium.org>, "p.zabel@...gutronix.de"
 <p.zabel@...gutronix.de>,  "matthias.bgg@...il.com"	
 <matthias.bgg@...il.com>
Cc: Ariel D'Alessandro <ariel.dalessandro@...labora.com>, 
 "dri-devel@...ts.freedesktop.org"	 <dri-devel@...ts.freedesktop.org>, Nancy
 Lin (林欣螢)	
 <Nancy.Lin@...iatek.com>, "linux-kernel@...r.kernel.org"	
 <linux-kernel@...r.kernel.org>, Jason-JH Lin
 (林睿祥)	 <Jason-JH.Lin@...iatek.com>,
 "linux-arm-kernel@...ts.infradead.org"	
 <linux-arm-kernel@...ts.infradead.org>, Daniel Stone
 <daniels@...labora.com>,  "linux-mediatek@...ts.infradead.org"	
 <linux-mediatek@...ts.infradead.org>, "kernel@...labora.com"	
 <kernel@...labora.com>
Subject: Re: [PATCH RFC 3/6] drm/mediatek: ovl: Fix misaligned layer source
 size on AFBC mode

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@...labora.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