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

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Message-ID: <3a2v2i5lximl6q7eidd5zhjoyckz2fvgv52rhjruiuyuc6v3a3@5kdqa2eypidt>
Date: Mon, 13 Oct 2025 17:34:06 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Junjie Cao <caojunjie650@...il.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

On Mon, Oct 13, 2025 at 09:17:04PM +0800, Junjie Cao wrote:
> 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.

Why do you need it in DT if the panel driver can provide this
information.

-- 
With best wishes
Dmitry