linux-kernel - Re: [PATCH] drm/mediatek: Disable AFBC support on Mediatek DRM driver

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20260210050606.GA852606@google.com>
Date: Tue, 10 Feb 2026 13:06:06 +0800
From: Chen-Yu Tsai <wenst@...omium.org>
To: Ariel D'Alessandro <ariel.dalessandro@...labora.com>
Cc: chunkuang.hu@...nel.org, p.zabel@...gutronix.de, airlied@...il.com,
	simona@...ll.ch, matthias.bgg@...il.com,
	angelogioacchino.delregno@...labora.com, greenjustin@...omium.org,
	sjoerd@...labora.com, dri-devel@...ts.freedesktop.org,
	linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, kernel@...labora.com,
	Macpaul Lin (林智斌) <Macpaul.Lin@...iatek.com>,
	Daniel Stone <daniels@...labora.com>
Subject: Re: [PATCH] drm/mediatek: Disable AFBC support on Mediatek DRM driver

Sorry for revisiting this old thread.

On Fri, Oct 24, 2025 at 05:27:56PM -0300, Ariel D'Alessandro wrote:
> Commit c410fa9b07c32 ("drm/mediatek: Add AFBC support to Mediatek DRM
> driver") added AFBC support to Mediatek DRM and enabled the
> 32x8/split/sparse modifier.
> 
> However, this is currently broken on Mediatek MT8188 (Genio 700 EVK
> platform); tested using upstream Kernel and Mesa (v25.2.1), AFBC is used by
> default since Mesa v25.0.
> 
> Kernel trace reports vblank timeouts constantly, and the render is garbled:
> 
> ```
> [CRTC:62:crtc-0] vblank wait timed out
> WARNING: CPU: 7 PID: 70 at drivers/gpu/drm/drm_atomic_helper.c:1835 drm_atomic_helper_wait_for_vblanks.part.0+0x24c/0x27c
> [...]
> Hardware name: MediaTek Genio-700 EVK (DT)
> Workqueue: events_unbound commit_work
> pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> pc : drm_atomic_helper_wait_for_vblanks.part.0+0x24c/0x27c
> lr : drm_atomic_helper_wait_for_vblanks.part.0+0x24c/0x27c
> sp : ffff80008337bca0
> x29: ffff80008337bcd0 x28: 0000000000000061 x27: 0000000000000000
> x26: 0000000000000001 x25: 0000000000000000 x24: ffff0000c9dcc000
> x23: 0000000000000001 x22: 0000000000000000 x21: ffff0000c66f2f80
> x20: ffff0000c0d7d880 x19: 0000000000000000 x18: 000000000000000a
> x17: 000000040044ffff x16: 005000f2b5503510 x15: 0000000000000000
> x14: 0000000000000000 x13: 74756f2064656d69 x12: 742074696177206b
> x11: 0000000000000058 x10: 0000000000000018 x9 : ffff800082396a70
> x8 : 0000000000057fa8 x7 : 0000000000000cce x6 : ffff8000823eea70
> x5 : ffff0001fef5f408 x4 : ffff80017ccee000 x3 : ffff0000c12cb480
> x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff0000c12cb480
> Call trace:
>  drm_atomic_helper_wait_for_vblanks.part.0+0x24c/0x27c (P)
>  drm_atomic_helper_commit_tail_rpm+0x64/0x80
>  commit_tail+0xa4/0x1a4
>  commit_work+0x14/0x20
>  process_one_work+0x150/0x290
>  worker_thread+0x2d0/0x3ec
>  kthread+0x12c/0x210
>  ret_from_fork+0x10/0x20
> ---[ end trace 0000000000000000 ]---
> ```
> 
> Until this gets fixed upstream, disable AFBC support on this platform, as
> it's currently broken with upstream Mesa.

Do you remember the circumstances you had an issue with?

Looking at our notes, it seems that for MT8188 only vdosys0 supports
AFBC. And on MT8195 it has issues with color correction on the second
pipeline. The driver as currently seen in next-20260209 only signals
AFBC support for the first pipeline on these two platforms. So I don't
see any issues there.

The commit you mentioned that introduces AFBC support failed to take
into account this flag when exposing AFBC support to userspace. But
this was subsequently fixed by:

    8d121a82fa56 drm/mediatek: only announce AFBC if really supported

On my MT8188 based Chromebook, only the planes for the internal display,
i.e. the first or vdosys0 pipeline, show AFBC support.

AFAICT the Genio 700 EVK only has one external HDMI connector, and that
is tied to the second pipeline, which should not have AFBC support
announced. I'm not sure why mesa would still be using AFBC then.


Thanks
ChenYu