linux-kernel - Re: [PATCH 2/3] drm/msm/dsi: support DSC configurations with slice_per

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Message-ID: <CAK6c68hZq2o9YXxzd2dv5AXw5-UfKv_58MoUrQfGyfPiONArEg@mail.gmail.com>
Date: Mon, 13 Oct 2025 21:17:04 +0800
From: Junjie Cao <caojunjie650@...il.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Neil Armstrong <neil.armstrong@...aro.org>, 
	Jessica Zhang <jessica.zhang@....qualcomm.com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Rob Clark <robin.clark@....qualcomm.com>, Dmitry Baryshkov <lumag@...nel.org>, 
	Abhinav Kumar <abhinav.kumar@...ux.dev>, Sean Paul <sean@...rly.run>, 
	Marijn Suijten <marijn.suijten@...ainline.org>, Antonino Maniscalco <antomani103@...il.com>, 
	Jonathan Marek <jonathan@...ek.ca>, Eugene Lepshy <fekz115@...il.com>, Jun Nie <jun.nie@...aro.org>, 
	dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org, 
	freedreno@...ts.freedesktop.org
Subject: Re: [PATCH 2/3] drm/msm/dsi: support DSC configurations with
 slice_per_pkt > 1

Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com> 于2025年10月13日周一 20:31写道：
> On Mon, Oct 13, 2025 at 07:04:43PM +0800, Junjie Cao wrote:
> > Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com> 于2025年10月13日周一 17:39写道：
> > > On 13/10/2025 04:52, 曹俊杰 wrote:
> > > >  >Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com
> > > > <mailto:dmitry.baryshkov@....qualcomm.com>> 于2025年10月2日周四 10:04写道：
> > > >  >On Wed, Oct 01, 2025 at 09:59:13PM +0800, Junjie Cao wrote:
> > > >  >> From: Jun Nie <jun.nie@...aro.org <mailto:jun.nie@...aro.org>>
> > > >  >>
> > > >  >> Some panels support multiple slice to be sent in a single DSC
> > > > packet. And
> > > >  >> this feature is a must for specific panels, such as JDI LPM026M648C.
> > > > Add a
> > > >  >> 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
> > > > <mailto:jonathan@...ek.ca>>
> > > >  >> Signed-off-by: Jonathan Marek <jonathan@...ek.ca
> > > > <mailto:jonathan@...ek.ca>>
> > > >  >> Signed-off-by: Jun Nie <jun.nie@...aro.org <mailto:jun.nie@...aro.org>>
> > > >  >> Signed-off-by: Junjie Cao <caojunjie650@...il.com
> > > > <mailto:caojunjie650@...il.com>>
> > > >  >> ---
> > > >  >>  drivers/gpu/drm/msm/dsi/dsi_host.c | 25 ++++++++++---------------
> > > >  >>  include/drm/drm_mipi_dsi.h         |  2 ++
> > > >  >>  2 files changed, 12 insertions(+), 15 deletions(-)
> > > >  >
> > > >  >Please extract the generic part, so that it can be merged through a
> > > >  >generic tree.
> > > >  >
> > > >
> > > > Sorry, I don't get it.  The generic part, generic tree? Do you mean
> > > > the drm tree? `slice_per_pkt >= 2` is seen on the panels of these
> > > > tablets that are equipped with qcom chips. I don't know if these
> > > > panels are used on other platforms, and if it is necessary to do it
> > > > in drm.
> > >
> > > There are two changes here:
> > > - MIPI DSI header change
> > > - msm DSI driver
> > >
> > > I've asked to split it to those two commits so that he change for
> > > drm_mipi_dsi.h is more obvious for reviewers and so that it can be
> > > merged through a drm-misc tree (or through drm-msm tree provided it gets
> > > a necessary ack).
> > >
> >
> > Thanks for your clear explanation.
> >
> > I don't mind to add the field separately. But should I submit it
> > with the panel driver together? Otherwise, this field is unused
> > for a while.
> >
> > However, as you mentioned, this is not a part of standard, neither
> > mipi dsi nor VESA DSC. Recently, only Qualcomm devices require it
> > to calculate parameters, then we use them to program registers. Why
> > don't we parse the field from devicetree?
>
> Because the value is uniquelly identified by the panel's compat string.
>

Yes, it is panel specified.
But can we set it for every panel like

&mdss_dsi0 {
    qcom,mdss-dsc-slice-per-pkt = <2>;

    status = "okay";

    panel: panel@0 {
        compatible = "foo,bar";
        reg = <0>;
    };
};

or moving the property to panel node? We access it from child node.

> --
> With best wishes
> Dmitry