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From:   Alex Deucher <alexdeucher@gmail.com>
Date:   Tue, 13 Feb 2018 10:19:35 -0500
Message-ID: <CADnq5_PSLqiZvYAc4DewM6cXEgsp_Qtkt27VWY_8Oro68GiozQ@mail.gmail.com>
Subject: Re: [PATCH 0/5] Fix deadlock on runtime suspend in DRM drivers
To:     Lukas Wunner <lukas@wunner.de>
Cc:     Mike Lothian <mike@fireburn.co.uk>,
        Ismo Toijala <ismo.toijala@gmail.com>,
        Hans de Goede <hdegoede@redhat.com>,
        nouveau <nouveau@lists.freedesktop.org>,
        Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Maling list - DRI developers 
        <dri-devel@lists.freedesktop.org>,
        Alex Deucher <alexander.deucher@amd.com>,
        Ben Skeggs <bskeggs@redhat.com>, Tejun Heo <tj@kernel.org>,
        Dave Airlie <airlied@redhat.com>,
        Liviu Dudau <Liviu.Dudau@arm.com>,
        Peter Wu <peter@lekensteyn.nl>
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On Tue, Feb 13, 2018 at 3:17 AM, Lukas Wunner <lukas@wunner.de> wrote:
> On Mon, Feb 12, 2018 at 01:58:32PM -0500, Alex Deucher wrote:
>> On Mon, Feb 12, 2018 at 4:45 AM, Lukas Wunner <lukas@wunner.de> wrote:
>> > On Mon, Feb 12, 2018 at 09:03:26AM +0000, Mike Lothian wrote:
>> >> On 12 February 2018 at 03:39, Lukas Wunner <lukas@wunner.de> wrote:
>> >> > On Mon, Feb 12, 2018 at 12:35:51AM +0000, Mike Lothian wrote:
>> >> > > I've not been able to reproduce the original problem you're trying to
>> >> > > solve on amdgpu thats with or without your patch set and the above
>> >> > > "trigger" too
>> >
>> > Okay the reason you're not seeing deadlocks is because the output poll
>> > worker is not enabled.  And the output poll worker is not enabled
>> > because your discrete GPU doesn't have any outputs:
>> >
>> > [    0.265568] [drm:dc_create] *ERROR* DC: Number of connectors is zero!
>> >
>> > The outputs are only polled if there are connectors which have the
>> > DRM_CONNECTOR_POLL_CONNECT or DRM_CONNECTOR_POLL_DISCONNECT flag set.
>> > And that only ever seems to be the case for VGA and DVI.
>> >
>> > We know based on bugzilla reports that hybrid graphics laptops do exist
>> > which poll outputs with radeon and nouveau.  If there are no laptops
>> > supported by amdgpu whose discrete GPU has polled connectors, then
>> > patch [5/5] would be unnecessary.  That is for Alex to decide.
>>
>> Most hybrid laptops don't have display connectors on the dGPU and we
>> only use polling on analog connectors, so you are not likely to run
>> into this on recent laptops.  That said, I don't know if there is some
>> OEM system out there with a VGA port on the dGPU in a hybrid laptop.
>> I guess another option is to just disable polling on hybrid laptops.
>
> If we don't know for sure, applying patch [5/5] would seem to be the
> safest approach.  (Assuming it doesn't break anything else.)


I don't have any objections.  I see no reason to leave out the amdgpu changes.

Alex