linux-kernel - Re: [PATCH 1/2] drm: introduce page_flip

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Message-ID: <17cd6378-e3fa-419b-90d3-7e0549817110@amd.com>
Date: Wed, 28 Jan 2026 11:39:59 +0100
From: Christian König <christian.koenig@....com>
To: Alex Deucher <alexdeucher@...il.com>,
 Hamza Mahfooz <someguy@...ective-light.com>
Cc: Mario Limonciello <mario.limonciello@....com>,
 Timur Kristóf <timur.kristof@...il.com>,
 dri-devel@...ts.freedesktop.org, Alex Deucher <alexander.deucher@....com>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Harry Wentland <harry.wentland@....com>, Leo Li <sunpeng.li@....com>,
 Rodrigo Siqueira <siqueira@...lia.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 Sunil Khatri <sunil.khatri@....com>, Ce Sun <cesun102@....com>,
 Lijo Lazar <lijo.lazar@....com>, Kenneth Feng <kenneth.feng@....com>,
 Ivan Lipski <ivan.lipski@....com>, Alex Hung <alex.hung@....com>,
 Tom Chung <chiahsuan.chung@....com>, Melissa Wen <mwen@...lia.com>,
 Michel Dänzer <mdaenzer@...hat.com>,
 Fangzhi Zuo <Jerry.Zuo@....com>, amd-gfx@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] drm: introduce page_flip_timeout()

On 1/27/26 23:57, Alex Deucher wrote:
> On Tue, Jan 27, 2026 at 5:53 PM Hamza Mahfooz
> <someguy@...ective-light.com> wrote:
>>
>> On Mon, Jan 26, 2026 at 09:20:55AM -0500, Alex Deucher wrote:
>>> I suspect just calling drm_crtc_send_vblank_event() here on the
>>> relevant crtcs would be enough.
>>>
>>
>> Seems like an interesting idea, though I would imagine we would still
>> want to attempt a reset (of some kind) assuming that the subsequent page
>> flip also experiences a timeout.
> 
> Is it actually a timeout or just missed interrupts?  I'm wondering if
> some power feature races with the modeset and causes the interrupt to
> get missed from time to time.

That is my strong suspicion as well.

Even if we missed a vblank interrupt that thing is reoccurring, so the worst thing that can happen is that we delayed reporting back success by one frame.

So something must have turned the CRTC fully off.

BTW: suspending the DAL or event resetting the GPU in such a callback are just hacks, don't be surprised if you run into things like NULL pointer dereferences etc....

Christian.

> 
> Alex