linux-kernel - Re: [RFC PATCH 02/13] dt-bindings: msm/dsi: Document Display Stream Compression (DSC) parameters

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Message-ID: <YKtWM+BYeIA+P+55@vkoul-mobl.Dlink>
Date:   Mon, 24 May 2021 13:00:59 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Rob Clark <robdclark@...il.com>, linux-arm-msm@...r.kernel.org,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jonathan Marek <jonathan@...ek.ca>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Abhinav Kumar <abhinavk@...eaurora.org>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, Rob Herring <robh+dt@...nel.org>,
        devicetree@...r.kernel.org
Subject: Re: [RFC PATCH 02/13] dt-bindings: msm/dsi: Document Display Stream
 Compression (DSC) parameters

On 21-05-21, 09:42, Bjorn Andersson wrote:
> On Fri 21 May 07:49 CDT 2021, Vinod Koul wrote:
> 
> > DSC enables streams to be compressed before we send to panel. This
> > requires DSC enabled encoder and a panel to be present. So we add this
> > information in board DTS and find if DSC can be enabled and the
> > parameters required to configure DSC are added to binding document along
> > with example
> > 
> > Signed-off-by: Vinod Koul <vkoul@...nel.org>
> > ---
> >  .../devicetree/bindings/display/msm/dsi.txt       | 15 +++++++++++++++
> >  1 file changed, 15 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/display/msm/dsi.txt b/Documentation/devicetree/bindings/display/msm/dsi.txt
> > index b9a64d3ff184..83d2fb92267e 100644
> > --- a/Documentation/devicetree/bindings/display/msm/dsi.txt
> > +++ b/Documentation/devicetree/bindings/display/msm/dsi.txt
> > @@ -48,6 +48,13 @@ Optional properties:
> >  - pinctrl-n: the "sleep" pinctrl state
> >  - ports: contains DSI controller input and output ports as children, each
> >    containing one endpoint subnode.
> > +- qcom,mdss-dsc-enabled: Display Stream Compression (DSC) is enabled
> > +- qcom,mdss-slice-height: DSC slice height in pixels
> > +- qcom,mdss-slice-width: DSC slice width in pixels
> > +- qcom,mdss-slice-per-pkt: DSC slices per packet
> > +- qcom,mdss-bit-per-component: DSC bits per component
> > +- qcom,mdss-bit-per-pixel: DSC bits per pixel
> > +- qcom,mdss-block-prediction-enable: Block prediction mode of DSC enabled
> >  
> >    DSI Endpoint properties:
> >    - remote-endpoint: For port@0, set to phandle of the connected panel/bridge's
> > @@ -188,6 +195,14 @@ Example:
> >  		qcom,master-dsi;
> >  		qcom,sync-dual-dsi;
> >  
> > +		qcom,mdss-dsc-enabled;
> 
> To me the activation of DSC seems to be a property of the panel.

I think there are three parts to the problem
1. Panel needs to support it
2. Host needs to support it
3. Someone needs to decide to use when both the above conditions are
met.

There are cases where above 1, 2 will be satisfied, but we might be okay
without DSC too.. so how to decide when to do DSC :)

I feel it is more of a system property. And I also think that these
parameters here are host configuration and not really for panel...

> 
> > +		qcom,mdss-slice-height = <16>;
> > +		qcom,mdss-slice-width = <540>;
> > +		qcom,mdss-slice-per-pkt = <1>;
> > +		qcom,mdss-bit-per-component = <8>;
> > +		qcom,mdss-bit-per-pixel = <8>;
> > +		qcom,mdss-block-prediction-enable;
> 
> Which of these properties relates to the DSC encoder and what needs to
> be agreed with the sink? Can't we derive e.g. bpp from the information
> we have from the attached panel already?

Let me go back and check on this a bit more

Thanks
-- 
~Vinod