linux-kernel - Re: [PATCH v2 2/2] drm/msm/dpu: Fix timeout issues on command mode panels

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Date:   Thu, 9 Dec 2021 18:02:40 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>, robdclark@...il.com
Cc:     sean@...rly.run, airlied@...ux.ie, daniel@...ll.ch,
        abhinavk@...eaurora.org, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, konrad.dybcio@...ainline.org,
        marijn.suijten@...ainline.org, martin.botka@...ainline.org,
        ~postmarketos/upstreaming@...ts.sr.ht, phone-devel@...r.kernel.org,
        paul.bouchara@...ainline.org
Subject: Re: [PATCH v2 2/2] drm/msm/dpu: Fix timeout issues on command mode
 panels

Il 02/10/21 00:33, Dmitry Baryshkov ha scritto:
> On 11/09/2021 19:39, AngeloGioacchino Del Regno wrote:
>> In function dpu_encoder_phys_cmd_wait_for_commit_done we are always
>> checking if the relative CTL is started by waiting for an interrupt
>> to fire: it is fine to do that, but then sometimes we call this
>> function while the CTL is up and has never been put down, but that
>> interrupt gets raised only when the CTL gets a state change from
>> 0 to 1 (disabled to enabled), so we're going to wait for something
>> that will never happen on its own.
>>
>> Solving this while avoiding to restart the CTL is actually possible
>> and can be done by just checking if it is already up and running
>> when the wait_for_commit_done function is called: in this case, so,
>> if the CTL was already running, we can say that the commit is done
>> if the command transmission is complete (in other terms, if the
>> interface has been flushed).
> 
> I've compared this with the MDP5 driver, where we always wait for PP_DONE 
> interrupt. Would it be enough to always wait for it (= always call 
> dpu_encoder_phys_cmd_wait_for_tx_complete())?
> 

This sets my delay record to reply to two months. Great achievement!

Jokes apart, yes it would make sense to do that, it's something that works
at least... but we should verify that such a thing doesn't break new platforms
(like sm8150 and newer).