Re: [PATCH v4 5/6] dt-bindings: display: add Unisoc's mipi dsi controller bindings

From: Maxime Ripard <maxime@cerno.tech>
To: Kevin Tang <kevin3.tang@gmail.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Sean Paul <sean@poorly.run>, David Airlie <airlied@linux.ie>,
	Daniel Vetter <daniel@ffwll.ch>, Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Orson Zhai <orsonzhai@gmail.com>,
	Chunyan Zhang <zhang.lyra@gmail.com>,
	"Linux-Kernel@Vger. Kernel. Org" <linux-kernel@vger.kernel.org>,
	ML dri-devel <dri-devel@lists.freedesktop.org>,
	devicetree@vger.kernel.org
Subject: Re: [PATCH v4 5/6] dt-bindings: display: add Unisoc's mipi dsi controller bindings
Date: Thu, 15 Apr 2021 10:42:30 +0200	[thread overview]
Message-ID: <20210415084230.moqxuy3caym3kupk@gilmour> (raw)
In-Reply-To: <CAFPSGXaQKeKMKC7MGXhxQErB_yh_eE8khk1hOrjHnuOH20Gg4Q@mail.gmail.com>

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On Fri, Apr 09, 2021 at 08:23:19AM +0800, Kevin Tang wrote:
> Maxime Ripard <maxime@cerno.tech> 于2021年4月7日周三 下午6:46写道：
> 
> > On Wed, Mar 31, 2021 at 09:49:14AM +0800, Kevin Tang wrote:
> > > Hi Maxime,
> > >
> > > Maxime Ripard <maxime@cerno.tech> 于2021年3月24日周三 下午7:13写道：
> > >
> > > > On Mon, Feb 22, 2021 at 09:28:21PM +0800, Kevin Tang wrote:
> > > > > From: Kevin Tang <kevin.tang@unisoc.com>
> > > > >
> > > > > Adds MIPI DSI Controller
> > > > > support for Unisoc's display subsystem.
> > > > >
> > > > > Cc: Orson Zhai <orsonzhai@gmail.com>
> > > > > Cc: Chunyan Zhang <zhang.lyra@gmail.com>
> > > > > Signed-off-by: Kevin Tang <kevin.tang@unisoc.com>
> > > > > Reviewed-by: Rob Herring <robh@kernel.org>
> > > > > ---
> > > > >  .../display/sprd/sprd,sharkl3-dsi-host.yaml   | 102
> > ++++++++++++++++++
> > > > >  1 file changed, 102 insertions(+)
> > > > >  create mode 100644
> > > >
> > Documentation/devicetree/bindings/display/sprd/sprd,sharkl3-dsi-host.yaml
> > > > >
> > > > > diff --git
> > > >
> > a/Documentation/devicetree/bindings/display/sprd/sprd,sharkl3-dsi-host.yaml
> > > >
> > b/Documentation/devicetree/bindings/display/sprd/sprd,sharkl3-dsi-host.yaml
> > > > > new file mode 100644
> > > > > index 000000000..d439f688f
> > > > > --- /dev/null
> > > > > +++
> > > >
> > b/Documentation/devicetree/bindings/display/sprd/sprd,sharkl3-dsi-host.yaml
> > > > > @@ -0,0 +1,102 @@
> > > > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > > > +%YAML 1.2
> > > > > +---
> > > > > +$id:
> > > > http://devicetree.org/schemas/display/sprd/sprd,sharkl3-dsi-host.yaml#
> > > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > > +
> > > > > +title: Unisoc MIPI DSI Controller
> > > > > +
> > > > > +maintainers:
> > > > > +  - Kevin Tang <kevin.tang@unisoc.com>
> > > > > +
> > > > > +properties:
> > > > > +  compatible:
> > > > > +    const: sprd,sharkl3-dsi-host
> > > > > +
> > > > > +  reg:
> > > > > +    maxItems: 1
> > > > > +
> > > > > +  interrupts:
> > > > > +    maxItems: 2
> > > > > +
> > > > > +  clocks:
> > > > > +    minItems: 1
> > > > > +
> > > > > +  clock-names:
> > > > > +    items:
> > > > > +      - const: clk_src_96m
> > > > > +
> > > > > +  power-domains:
> > > > > +    maxItems: 1
> > > > > +
> > > > > +  ports:
> > > > > +    type: object
> > > > > +
> > > > > +    properties:
> > > > > +      "#address-cells":
> > > > > +        const: 1
> > > > > +
> > > > > +      "#size-cells":
> > > > > +        const: 0
> > > > > +
> > > > > +      port@0:
> > > > > +        type: object
> > > > > +        description:
> > > > > +          A port node with endpoint definitions as defined in
> > > > > +
> > Documentation/devicetree/bindings/media/video-interfaces.txt.
> > > > > +          That port should be the input endpoint, usually coming
> > from
> > > > > +          the associated DPU.
> > > > > +      port@1:
> > > > > +        type: object
> > > > > +        description:
> > > > > +          A port node with endpoint definitions as defined in
> > > > > +
> > Documentation/devicetree/bindings/media/video-interfaces.txt.
> > > > > +          That port should be the output endpoint, usually output to
> > > > > +          the associated panel.
> > > >
> > > > The DSI generic binding asks that peripherals that are controlled
> > > > through a DCS be a subnode of the MIPI-DSI bus, not through a port
> > > > endpoint.
> > > >
> > >  Our DSI controller don't support DCS now...
> >
> > I'm not sure I follow you, you mentionned in the patch 4 that you were
> > testing for a device to be in command mode, how would that work without
> > DCS support?
> >
> Sorry, I see DCS as DSC, pls ignore my previous comments.
> 
> dsi input node is display controller and dsi output node is panel,
> I still don't understand what it has to do with dcs? and it seems that
> other vendors also like this.
> 
> can you help provide some cases?

So the device tree is a tree organized through which bus controls which
device: Your DSI controller is accessed through a memory-mapped region
and is thus a child node of the main bus (I guess?) and then, since the
DSI panel is going to be controlled through the DSI controller and
MIPI-DCS, it needs to be a child of the display controller.

This is exactly what is being described here:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/display/mipi-dsi-bus.txt#n42

The second port is thus not needed at all

Maxime

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