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

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Date:   Wed, 22 Dec 2021 12:54:41 +0100
From:   Marijn Suijten <marijn.suijten@...ainline.org>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>
Cc:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        robdclark@...il.com, 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, 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

On 2021-12-22 12:28:52, AngeloGioacchino Del Regno wrote:
> Il 11/12/21 22:57, Marijn Suijten ha scritto:
> > On 2021-12-12 00:49:09, Dmitry Baryshkov wrote:
> >> On Sun, 12 Dec 2021 at 00:35, Marijn Suijten
> >> <marijn.suijten@...ainline.org> wrote:
> >>> [..]
> >>> On this note, does it perhaps make more sense to call the "internal"
> >>> _dpu_encoder_phys_cmd_wait_for_idle function directly, instead of going
> >>> through the "public" dpu_encoder_phys_cmd_wait_for_tx_complete which
> >>> seems solely intended to handle the wait_for_tx_complete callback?
> >>
> >> Either one would work. The main difference is the error message. Do
> >> you want to see it here if the wait times out or not?
> > 
> > I prefer calling _dpu_encoder_phys_cmd_wait_for_idle directly and
> > optionally adding our own error message.  IIRC DRM_ERROR prints source
> > information such as the function this originated from, and that makes it
> > impossible to distinguish between the wait_for_tx_complete callback or
> > the invocation through dpu_encoder_phys_cmd_wait_for_commit_done anyway.
> > 
> > - Marijn
> > 
> 
> I wouldn't be happy to find myself in a situation in which I get strange
> display slowness without any print to help me; for this reason, I find
> having the print in place useful for debugging of both perf and fault.

Same thought here, though dpu_encoder_phys_cmd_wait_for_tx_complete
exists for the sole reason of printing a nice debug message, which I
wouldn't want to be misused by dpu_encoder_phys_cmd_wait_for_commit_done
punting its errors on wait_for_tx_complete - if that happens the first
thing I'd do during debugging is assign individual messages to both,
otherwise it is impossible to know which two functions is the cause: we
might as well "duplicate" the error message right now and prevent such
confusion from occurring in the first place?

- Marijn

> 
> Cheers,
> - Angelo