linux-kernel - Re: [PATCH v2 1/9] dt-bindings: display: sun4i: Add component endpoint ID numbering scheme

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Date:   Tue, 2 May 2017 16:54:53 +0200
From:   Maxime Ripard <maxime.ripard@...e-electrons.com>
To:     Rob Herring <robh@...nel.org>
Cc:     Chen-Yu Tsai <wens@...e.org>, David Airlie <airlied@...ux.ie>,
        Mark Rutland <mark.rutland@....com>,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-sunxi@...glegroups.com
Subject: Re: [PATCH v2 1/9] dt-bindings: display: sun4i: Add component
 endpoint ID numbering scheme

Hi,

On Fri, Apr 28, 2017 at 08:48:41AM -0500, Rob Herring wrote:
> On Fri, Apr 21, 2017 at 04:38:49PM +0800, Chen-Yu Tsai wrote:
> > The Allwinner display pipeline contains many hardware components, some
> > of which can consume data from one of multiple upstream components.
> > The numbering scheme of these components must be encoded into the device
> > tree so the driver can figure out which component out of two or more of
> > the same type it is supposed to use or program.
> > 
> > This patch adds the constraint that local endpoint IDs must be the index
> > or number of the remote endpoint's hardware block, for all components
> > in the display pipeline up to the TCONs.
> > 
> > Signed-off-by: Chen-Yu Tsai <wens@...e.org>
> > ---
> >  Documentation/devicetree/bindings/display/sunxi/sun4i-drm.txt | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/display/sunxi/sun4i-drm.txt b/Documentation/devicetree/bindings/display/sunxi/sun4i-drm.txt
> > index 57a8d0610062..7acdbf14ae1c 100644
> > --- a/Documentation/devicetree/bindings/display/sunxi/sun4i-drm.txt
> > +++ b/Documentation/devicetree/bindings/display/sunxi/sun4i-drm.txt
> > @@ -4,6 +4,16 @@ Allwinner A10 Display Pipeline
> >  The Allwinner A10 Display pipeline is composed of several components
> >  that are going to be documented below:
> >  
> > +For the input port of all components up to the TCON in the display
> > +pipeline, if there are multiple components, the local endpoint IDs
> > +must correspond to the index of the upstream block. For example, if
> > +the remote endpoint is Frontend 1, then the local endpoint ID must
> > +be 1.
> > +
> > +Conversely, for the output ports of the same group, the remote endpoint
> > +ID must be the index of the local hardware block. If the local backend
> > +is backend 1, then the remote endpoint ID must be 1.
> 
> It would be clearer if you just explicitly listed IDs and their 
> connections. From how this is worded, it would not work if you had 
> connections like this:
> 
> DevA 0
> DevA 1
> DevB 0
> DevB 1
> 
> These would need to be endpoints 0-3 in TCON, and that doesn't reflect 
> the remote devices' index.

Chen-Yu, can you send a patch to rephrase the doc that way?

Thanks,
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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