linux-kernel - Re: [PATCH 5/7] drm/msm/dpu: Correct dual-ctl -> dual-intf typo in comment

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Message-ID: <mrg3m7awzvozhyg2zwwbawfa6cb6xo7obzooiq3iph6mu3ybfc@b5h2pzxvcjvf>
Date: Sun, 28 Apr 2024 23:06:34 +0200
From: Marijn Suijten <marijn.suijten@...ainline.org>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Rob Clark <robdclark@...il.com>, 
	Abhinav Kumar <quic_abhinavk@...cinc.com>, Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>, 
	Daniel Vetter <daniel@...ll.ch>, Archit Taneja <architt@...eaurora.org>, 
	Chandan Uddaraju <chandanu@...eaurora.org>, Vinod Koul <vkoul@...nel.org>, 
	Sravanthi Kollukuduru <skolluku@...eaurora.org>, linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	Jordan Crouse <jordan@...micpenguin.net>, Rajesh Yadav <ryadav@...eaurora.org>, 
	Jeykumar Sankaran <jsanka@...eaurora.org>, ~postmarketos/upstreaming@...ts.sr.ht, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, Konrad Dybcio <konrad.dybcio@...aro.org>, 
	Martin Botka <martin.botka@...ainline.org>, Jami Kettunen <jami.kettunen@...ainline.org>
Subject: Re: [PATCH 5/7] drm/msm/dpu: Correct dual-ctl -> dual-intf typo in
 comment

On 2024-04-18 02:30:59, Dmitry Baryshkov wrote:
> On Wed, Apr 17, 2024 at 01:57:45AM +0200, Marijn Suijten wrote:
> > This comment one line down references a single, "same CTL" that controls
> > two interfaces, so the comment should clearly describe two interfaces
> > used with a single active CTL and not "two CTLs".
> > 
> > Fixes: 25fdd5933e4c ("drm/msm: Add SDM845 DPU support")
> > Signed-off-by: Marijn Suijten <marijn.suijten@...ainline.org>
> > ---
> >  drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
> > index d9e7dbf0499c..7e849fe74801 100644
> > --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
> > +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
> > @@ -428,7 +428,7 @@ static void dpu_encoder_phys_vid_enable(struct dpu_encoder_phys *phys_enc)
> >  	dpu_encoder_phys_vid_setup_timing_engine(phys_enc);
> >  
> >  	/*
> > -	 * For single flush cases (dual-ctl or pp-split), skip setting the
> > +	 * For single flush cases (dual-intf or pp-split), skip setting the
> 
> It should be fixed, but in the other way: it's 'single-ctl'. See
> sde_encoder_phys_needs_single_flush().

As written in the cover letter I was unsure about this comment.

You are right that sde_encoder_phys_needs_single_flush() is supposed to return
true in pp-split or single-ctl.  However, the second part of the comment (right
below) is in conflict with another patch that I've sent as part of these series:
on a single-ctl setup with dual interfaces, the second INTF needs to be marked
for flushing.

While that observation and fix is for CMD-mode, the exact same comment is found
downstream for video mode:

https://git.codelinaro.org/clo/la/platform/vendor/opensource/display-drivers/-/blob/display-kernel.lnx.5.4.r1-rel/msm/sde/sde_encoder_phys_vid.c?ref_type=heads#L794-804

You were fixing exactly that in one of your preliminary Active-CTL patches by
making dpu_encoder_phys_vid_needs_single_flush() return for Active-CTL, so we
should probably update this comment in the same patch when you send it?

(that is: the flush bit needs to be set for the slave intf in Active-CTL. Before
Active-CTL, a slave encoder would actually have two CTLs and two INTFs where the
flush bit was probably skipped on both slaves?)

On a side-note, since the needs_single_flush callback is used elsehwere, I'm
unsure if that patch affects things in the wrong way since the downstream file
linked above applies the check for CTL_ACTIVE_CFG directly in-line without
affecting the callback.

- Marijn

> >  	 * flush bit for the slave intf, since both intfs use same ctl
> >  	 * and HW will only flush the master.
> >  	 */
> > 
> > -- 
> > 2.44.0
> > 
> 
> -- 
> With best wishes
> Dmitry