Re: [PATCH 06/11] dt-bindings: display: sun4i-drm: Add A83T HDMI pipeline

[Icenowy Zheng]

ä 2018å1æ5æ GMT+08:00 äå2:52:10, Maxime Ripard <maxime.ripard@xxxxxxxxxxxxxxxxxx> åå:
>On Wed, Jan 03, 2018 at 10:32:26PM +0100, Jernej Åkrabec wrote:
>> Hi Rob,
>> 
>> Dne sreda, 03. januar 2018 ob 21:21:54 CET je Rob Herring napisal(a):
>> > On Sat, Dec 30, 2017 at 10:01:58PM +0100, Jernej Skrabec wrote:
>> > > This commit adds all necessary compatibles and descriptions
>needed to
>> > > implement A83T HDMI pipeline.
>> > > 
>> > > Mixer is already properly described, so only compatible is added.
>> > > 
>> > > However, A83T TCON1, which is connected to HDMI, doesn't have
>channel 0,
>> > > contrary to all TCONs currently described. Because of that, TCON
>> > > documentation is extended.
>> > > 
>> > > A83T features Synopsys DW HDMI controller with a custom PHY which
>looks
>> > > like Synopsys Gen2 PHY with few additions. Since there is no
>> > > documentation, needed properties were found out through
>experimentation
>> > > and reading BSP code.
>> > > 
>> > > At the end, example is added for newer SoCs, which features DE2
>and DW
>> > > HDMI.
>> > > 
>> > > Signed-off-by: Jernej Skrabec <jernej.skrabec@xxxxxxxx>
>> > > ---
>> > > 
>> > >  .../bindings/display/sunxi/sun4i-drm.txt           | 188
>> > >  ++++++++++++++++++++- 1 file changed, 181 insertions(+), 7
>deletions(-)
>> > > 
>> > > diff --git
>a/Documentation/devicetree/bindings/display/sunxi/sun4i-drm.txt
>> > > b/Documentation/devicetree/bindings/display/sunxi/sun4i-drm.txt
>index
>> > > 9f073af4c711..3eca258096a5 100644
>> > > ---
>a/Documentation/devicetree/bindings/display/sunxi/sun4i-drm.txt
>> > > +++
>b/Documentation/devicetree/bindings/display/sunxi/sun4i-drm.txt
>> > > 
>> > > @@ -64,6 +64,40 @@ Required properties:
>> > >      first port should be the input endpoint. The second should
>be the
>> > >      output, usually to an HDMI connector.
>> > > 
>> > > +DWC HDMI TX Encoder
>> > > +-----------------------------
>> > > +
>> > > +The HDMI transmitter is a Synopsys DesignWare HDMI 1.4 TX
>controller IP
>> > > +with Allwinner's own PHY IP. It supports audio and video outputs
>and CEC.
>> > > +
>> > > +These DT bindings follow the Synopsys DWC HDMI TX bindings
>defined in
>> > > +Documentation/devicetree/bindings/display/bridge/dw_hdmi.txt
>with the
>> > > +following device-specific properties.
>> > > +
>> > > +Required properties:
>> > > +
>> > > +  - compatible: value must be one of:
>> > > +    * "allwinner,sun8i-a83t-dw-hdmi"
>> > > +  - reg: two pairs of base address and size of memory-mapped
>region,
>> > > first
>> > > +    for controller and second for PHY
>> > > +    registers.
>> > 
>> > Seems like the phy should be a separate node and use the phy
>binding.
>> > You can use the phy binding even if you don't use the kernel phy
>> > framework...
>> 
>> Unfortunately, it's not so straighforward. Phy is actually accessed
>through 
>> I2C implemented in HDMI controller. Second memory region in this case
>has 
>> small influence on phy. However, it has big influence on controller.
>For 
>> example, magic number has to be written in one register in second
>memory 
>> region in order to unlock read access to any register from first
>memory region 
>> (controller). However, they shouldn't be merged to one region,
>because first 
>> memory region requires byte access while second memory region can be
>accessed 
>> per byte or word.
>> 
>> To complicate things more, later I want to add support for another
>SoC which 
>> has same glue layer (unlocking read access, etc.) and uses memory
>mapped phy 
>> registers in second memory region.
>> 
>> I think current binding is the least complicated way to represent
>this.
>
>I agree with Rob here. I did a similar thing for the DSI patches I've
>sent a few monthes ago and it turned out to not be that difficult, so
>I'm sure you can come up with something :)

In A83T/H3/A64/H5/R40 this part is not purely a PHY.
It controls the access of main controller's register (e.g. read/write
lock and register obfuscation). So it should be called a "glue"
with PHY part (and on A83T seems a pure glue) but not a simple
 PHY.

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