linux-kernel - Re: [PATCH 1/6] dt-bindings: display: add Unisoc's drm master bindings

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Date:   Tue, 1 Dec 2020 10:36:54 -0700
From:   Rob Herring <robh+dt@...nel.org>
To:     Kevin Tang <kevin3.tang@...il.com>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Mark Rutland <mark.rutland@....com>,
        Orson Zhai <orsonzhai@...il.com>,
        Lyra Zhang <zhang.lyra@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH 1/6] dt-bindings: display: add Unisoc's drm master bindings

On Tue, Dec 1, 2020 at 12:36 AM Kevin Tang <kevin3.tang@...il.com> wrote:
>
> Hi Rob
>
> Rob Herring <robh+dt@...nel.org> 于2020年12月1日周二 上午4:29写道：
> >
> > On Mon, Nov 30, 2020 at 7:28 AM Kevin Tang <kevin3.tang@...il.com> wrote:
> > >
> > > From: Kevin Tang <kevin.tang@...soc.com>
> >
> > Once again, DT patches must Cc the DT list if you want them reviewed.
> Ok, i will add DT list to my Cc list.
> >
> > >
> > > The Unisoc DRM master device is a virtual device needed to list all
> > > DPU devices or other display interface nodes that comprise the
> > > graphics subsystem
> > >
> > > Cc: Orson Zhai <orsonzhai@...il.com>
> > > Cc: Chunyan Zhang <zhang.lyra@...il.com>
> > > Signed-off-by: Kevin Tang <kevin.tang@...soc.com>
> > > ---
> > >  .../display/sprd/sprd,display-subsystem.yaml       | 39 ++++++++++++++++++++++
> > >  1 file changed, 39 insertions(+)
> > >  create mode 100644 Documentation/devicetree/bindings/display/sprd/sprd,display-subsystem.yaml
> > >
> > > diff --git a/Documentation/devicetree/bindings/display/sprd/sprd,display-subsystem.yaml b/Documentation/devicetree/bindings/display/sprd/sprd,display-subsystem.yaml
> > > new file mode 100644
> > > index 0000000..9487a39
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/display/sprd/sprd,display-subsystem.yaml
> > > @@ -0,0 +1,39 @@
> > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > +%YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/display/sprd/sprd,display-subsystem.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: Unisoc DRM master device
> > > +
> > > +maintainers:
> > > +  - Kevin Tang <kevin.tang@...soc.com>
> > > +
> > > +description: |
> > > +  The Unisoc DRM master device is a virtual device needed to list all
> > > +  DPU devices or other display interface nodes that comprise the
> > > +  graphics subsystem.
> > > +
> > > +properties:
> > > +  compatible:
> > > +    const: sprd,display-subsystem
> >
> > As I said before, we try to avoid these virtual nodes. Make the DRM
> > driver bind to the DPU node.
> >
> > The case where this might be needed is if you have h/w that's a
> > mixture of shared and discrete blocks. I don't see anything here
> > matching that.
>
> This is how I understand this sentence: "h/w that's a mixture of shared and discrete blocks"
> We have multiple display controllers and corresponding physical interfaces, typical dual-screen display scenario
> E.g:
> 1. dpu0 and dpu1 both binding to DSI for dual mipi-dsi display;
> 2. dpu0 binding to DSI for primary display, and dpu1 binding to DP for external display;
>
> It looks like this:
> dpu0------>MIPI-DSI------>DPHY/CPHY Combo------>Panel0
>                         ^
>     ----------------|
>     |
> dpu1------>DisplayPort------>PHY------>Panel1
>
> For DTS like this:
> display-subsystem {
> compatible = "sprd,display-subsystem";
> ports = <&dpu0_out>, <&dpu1_out>;
> };

Yeah, this would be one such case. Just make this scenario clear in
commit message.

Rob