linux-kernel - Re: [PATCH v3 1/3] drm/msm/dsi: support DSC configurations with slice_per

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Message-ID: <wttg6aizzolsm7qqntspmmwje7kqfaayoqvwp76tvudlkx5phl@7twddmdajfwp>
Date: Fri, 26 Sep 2025 00:47:59 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Jun Nie <jun.nie@...aro.org>
Cc: Rob Clark <robin.clark@....qualcomm.com>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Jessica Zhang <jessica.zhang@....qualcomm.com>,
        Dmitry Baryshkov <lumag@...nel.org>, Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Krishna Manikandan <quic_mkrishn@...cinc.com>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, Jonathan Marek <jonathan@...ek.ca>
Subject: Re: [PATCH v3 1/3] drm/msm/dsi: support DSC configurations with
 slice_per_pkt > 1

On Thu, Sep 25, 2025 at 03:07:28PM +0800, Jun Nie wrote:
> Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com> 于2025年9月25日周四 03:10写道：
> >
> > On Wed, Sep 24, 2025 at 11:08:10PM +0800, Jun Nie wrote:
> > > Some panels support multiple slice to be sent in a single DSC packet. And
> >
> > s/support/require/
> >
> > If the panel supports something, then we can omit that and send 1 slice
> > as we currently do. If the panel requires multiple slices, it's
> > mandatory.
> >
> > > this feature is a must for specific panels, such as JDI LPM026M648C. Add a
> >
> > A panel driver which executes this API is appreciated. Otherwise in a
> > few months / years somebody will submit a patch 'field foo is not used
> > by the kernel drivers, drop it'.
> 
> OK, will add a panel driver in next version.
> >
> > > dsc_slice_per_pkt member into struct mipi_dsi_device and support the
> > > feature in msm mdss driver.
> > >
> > > Co-developed-by: Jonathan Marek <jonathan@...ek.ca>
> > > Signed-off-by: Jonathan Marek <jonathan@...ek.ca>
> > > Signed-off-by: Jun Nie <jun.nie@...aro.org>
> > > ---
> > >  drivers/gpu/drm/msm/dsi/dsi_host.c | 25 ++++++++++---------------
> > >  include/drm/drm_mipi_dsi.h         |  2 ++
> > >  2 files changed, 12 insertions(+), 15 deletions(-)
> > >
> > > @@ -196,6 +197,7 @@ struct mipi_dsi_device {
> > >       unsigned long hs_rate;
> > >       unsigned long lp_rate;
> > >       struct drm_dsc_config *dsc;
> > > +     unsigned int dsc_slice_per_pkt;
> >
> > Why is it a part of the DSI device config? What if a device specifies
> > dsc_slice_per_pkt, but not DSC config? What are the legit boundaries for
> > this field?
> 
> You are right. drm_dsc_config is better place to add the info. Thus only
> panels that support DSC can convey the info to host.

You will have to explain that it is not a part of the standard and what
kind of effect should it cause for DP and HDMI.

> >
> > >  };
> > >
> > >  /**
> > >
> > > --
> > > 2.34.1
> > >
> >
> > --
> > With best wishes
> > Dmitry

-- 
With best wishes
Dmitry