From: Matthieu CHARETTE <matthieu.charette@gmail.com>
To: Jani Nikula <jani.nikula@intel.com>
Cc: intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org
Subject: Re: [PATCH] drm/edid/firmware: stop using throwaway platform device
Date: Sun, 06 Nov 2022 16:03:00 +0100 [thread overview]
Message-ID: <0TLXKR.MU9V2CJGXH05@gmail.com> (raw)
In-Reply-To: <HBHNJR.ME9DMISWT3961@gmail.com>
Hi,
Can you tell me what are we waiting for? Maybe I can help.
Thanks.
Matthieu
On Wed, Oct 12 2022 at 07:16:29 PM +0200, Matthieu CHARETTE
<matthieu.charette@gmail.com> wrote:
> By crash, I mean that an error is returned here:
> https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux.git/+/refs/heads/master/drivers/gpu/drm/drm_edid_load.c#195
> I don't really know what happens next, but on my machine the built-in
> screen and the external remains dark. Also the kernel seems to
> freeze. I suspect a kernel panic, but I'm not sure. Anyway, the error
> is definitely not well handled, and a fix would be great.
> Also, request_firmware() will crash if called for the first time on
> the resume path because the file system isn't reachable on the resume
> process. And no cache is available for this firmware. So I guess that
> in this case, request_firmware() returns an error.
> Suspend-plug-resume case is not my priority nether as long as it
> doesn't make the system crash (Which is currently the case).
>
> On Wed, Oct 12 2022 at 11:25:59 AM +0300, Jani Nikula
> <jani.nikula@intel.com> wrote:
>> On Tue, 11 Oct 2022, Matthieu CHARETTE <matthieu.charette@gmail.com>
>> \x7fwrote:
>>> Currently the EDID is requested during the resume. But since it's
>>> requested too early, this means before the filesystem is mounted,
>>> \x7f\x7fthe
>>> firmware request fails. This make the DRM driver crash when
>>> \x7f\x7fresuming.
>>> This kind of issue should be prevented by the firmware caching
>>> \x7f\x7fprocess
>>> which cache every firmware requested for the next resume. But
>>> since \x7f\x7fwe
>>> are using a temporary device, the firmware isn't cached on suspend
>>> since the device doesn't work anymore.
>>> When using a non temporary device to get the EDID, the firmware
>>> will
>>> be cached on suspend for the next resume. So requesting the
>>> firmware
>>> during resume will succeed.
>>> But if the firmware has never been requested since the boot, this
>>> means that the monitor isn't plugged since the boot. The kernel
>>> will
>>> not be caching the EDID. So if we plug the monitor while the
>>> machine
>>> is suspended. The resume will fail to load the firmware. And the
>>> DRM
>>> driver will crash.
>>> So basically, your fix should solve the issue except for the case
>>> where the monitor hasn't been plugged since boot and is plugged
>>> \x7f\x7fwhile
>>> the machine is suspended.
>>> I hope I was clear. Tell me if I wasn't. I'm not really good at
>>> \x7f\x7fexplaining.
>>
>> That was a pretty good explanation. The only thing I'm missing is
>> what
>> the failure mode is exactly when you claim the driver will crash. Why
>> would request_firmware() "crash" if called for the first time on the
>> resume path?
>>
>> I'm not sure I care much about not being able to load the firmware
>> \x7fEDID
>> in the suspend-plug-resume case (as this can be remedied with a
>> subsequent modeset), but obviously any errors need to be handled
>> gracefully, without crashing.
>>
>> BR,
>> Jani.
>>
>>
>> --
>> Jani Nikula, Intel Open Source Graphics Center
>
>
next prev parent reply other threads:[~2022-11-06 15:03 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-06 22:21 [PATCH] drm/edid/firmware: stop using throwaway platform device Jani Nikula
2022-10-11 6:27 ` Matthieu CHARETTE
2022-10-11 7:20 ` Jani Nikula
2022-10-11 20:45 ` Matthieu CHARETTE
2022-10-12 8:25 ` Jani Nikula
2022-10-12 17:16 ` Matthieu CHARETTE
2022-11-06 15:03 ` Matthieu CHARETTE [this message]
2022-11-08 11:27 ` Jani Nikula
2022-11-08 15:40 ` Matthieu CHARETTE
2022-11-13 19:26 ` Matthieu CHARETTE
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