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From:   Rob Herring <robh@kernel.org>
Date:   Tue, 14 Aug 2018 08:39:00 -0600
Message-ID: <CAL_JsqJFmhKpcSKGfym+YtVAP24sPi1VLkM5EuRoJ-rkBG6EsA@mail.gmail.com>
Subject: Re: [PATCH v2 2/4] dt-bindings: soc: amlogic: add meson-canvas documentation
To:     Maxime Jourdan <maxi.jourdan@wanadoo.fr>
Cc:     Kevin Hilman <khilman@baylibre.com>,
        Neil Armstrong <narmstrong@baylibre.com>,
        Jerome Brunet <jbrunet@baylibre.com>,
        linux-amlogic@lists.infradead.org,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        devicetree@vger.kernel.org
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On Mon, Aug 13, 2018 at 8:42 PM Maxime Jourdan <maxi.jourdan@wanadoo.fr> wrote:
>
> 2018-08-13 21:07 GMT+02:00 Rob Herring <robh@kernel.org>:
> > On Wed, Aug 08, 2018 at 12:00:09AM +0200, Maxime Jourdan wrote:
> >> DT bindings doc for amlogic,meson-canvas
> >>
> >> Signed-off-by: Maxime Jourdan <maxi.jourdan@wanadoo.fr>
> >> ---
> >>  .../soc/amlogic/amlogic,meson-canvas.txt      | 36 +++++++++++++++++++
> >>  1 file changed, 36 insertions(+)
> >>  create mode 100644 Documentation/devicetree/bindings/soc/amlogic/amlogic,meson-canvas.txt
> >>
> >> diff --git a/Documentation/devicetree/bindings/soc/amlogic/amlogic,meson-canvas.txt b/Documentation/devicetree/bindings/soc/amlogic/amlogic,meson-canvas.txt
> >> new file mode 100644
> >> index 000000000000..5f0351717bee
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/soc/amlogic/amlogic,meson-canvas.txt
> >> @@ -0,0 +1,36 @@
> >> +Amlogic Canvas
> >> +================================
> >> +
> >> +A canvas is a collection of metadata that describes a pixel buffer.
> >> +Those metadata include: width, height, phyaddr, wrapping, block mode
> >> +and endianness.
> >> +
> >> +Many IPs within Amlogic SoCs rely on canvas indexes to read/write pixel data
> >> +rather than use the phy addresses directly. For instance, this is the case for
> >> +the video decoders and the display.
> >> +
> >> +Amlogic SoCs have 256 canvas.
> >> +
> >> +Device Tree Bindings:
> >> +---------------------
> >> +
> >> +Canvas Provider
> >> +--------------------------
> >> +
> >> +Required properties:
> >> +- compatible: "amlogic,canvas"
> >> +
> >> +Parent node should have the following properties :
> >> +- compatible: "amlogic,gx-dmc-sysctrl", "syscon", "simple-mfd"
> >
> > Is this documented somewhere? One child function is not a reason for an
> > MFD and child nodes. And child nodes like this with no resources are
> > unnecessary.
> >
>
> Hi Rob, this was done to follow the same path as other buses on the
> platform that have sysctrls in order to provide regmaps to the
> devices.
>
> I can see how it's not really necessary here though, would it be okay
> with you if I turned "canvas" into a simple bus subnode, using __iomem
> in the device ?

That's a driver issue that has little to do with the binding. You can
create a regmap for any node, "syscon" just does that automagically
for you.

Rob