linux-kernel - Re: [PATCH v3 05/15] drm/msm/dpu: fix mixer number counter on allocation

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Message-ID: <k2tf3tnaquagm7stxho7lrqj5oylbti4jisenm6t53hj5kvyhs@degtp25bmkj5>
Date: Thu, 9 Jan 2025 14:15:49 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Jun Nie <jun.nie@...aro.org>
Cc: Jessica Zhang <quic_jesszhan@...cinc.com>, 
	Rob Clark <robdclark@...il.com>, Abhinav Kumar <quic_abhinavk@...cinc.com>, 
	Sean Paul <sean@...rly.run>, Marijn Suijten <marijn.suijten@...ainline.org>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, linux-arm-msm@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 05/15] drm/msm/dpu: fix mixer number counter on
 allocation

On Thu, Jan 09, 2025 at 12:40:23PM +0800, Jun Nie wrote:
> Jessica Zhang <quic_jesszhan@...cinc.com> 于2025年1月9日周四 09:29写道：
> >
> >
> >
> > On 12/18/2024 11:49 PM, Jun Nie wrote:
> > > Add the case to reserve multiple pairs mixers for high resolution.
> > > Current code only supports one pair of mixer usage case. To support
> > > quad-pipe usage case, two pairs of mixers are needed.
> > >
> > > Current code resets number of mixer on failure of pair's peer test and
> > > retry on another pair. If two pairs are needed, the failure on the test
> > > of 2nd pair results clearing to the 1st pair. This patch only clear the
> > > bit for the 2nd pair allocation before retry on another pair.
> >
> > Hi Jun,
> >
> > I think the commit message wording is a bit unclear. Maybe something
> > like "Reset the current lm_count to an even number instead of completely
> > clearing it. This prevents all pairs from being cleared in cases where
> > multiple LM pairs are needed"
> 
> Thanks for the suggestion! Will adopt it.
> >
> > >
> > > Signed-off-by: Jun Nie <jun.nie@...aro.org>
> > > ---
> > >   drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c | 6 +++++-
> > >   1 file changed, 5 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c
> > > index cde3c5616f9bc..a8b01b78c02c7 100644
> > > --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c
> > > +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c
> > > @@ -316,7 +316,11 @@ static int _dpu_rm_reserve_lms(struct dpu_rm *rm,
> > >               if (!rm->mixer_blks[i])
> > >                       continue;
> > >
> > > -             lm_count = 0;
> > > +             /*
> > > +              * Clear the last bit to drop the previous primary mixer if
> > > +              * fail to find its peer.
> >
> > Same here can we reword it to something like "Reset lm_count to an even
> > index. This will drop the previous primary mixer if ..."
> 
> Will do.
> 
> >
> > > +              */
> > > +             lm_count &= 0xfe;
> >
> > Nit: Can we directly clear the first bit instead of doing an 8-bit bitmask?
> 
> Could you elaborate on it? Or you are suggesting to mask 0xFFFFFFFE?

I assume it is &= ~1

> 
> - Jun
> 
> >
> > Thanks,
> >
> > Jessica Zhang
> >
> > >               lm_idx[lm_count] = i;
> > >
> > >               if (!_dpu_rm_check_lm_and_get_connected_blks(rm, global_state,
> > >
> > > --
> > > 2.34.1
> > >
> >

-- 
With best wishes
Dmitry