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Date:   Fri, 01 Mar 2019 19:40:42 -0300
From:   Paul Cercueil <paul@...pouillou.net>
To:     Sam Ravnborg <sam@...nborg.org>
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>, devicetree@...r.kernel.org,
        linux-mips@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] dt-bindings: Add doc for the ingenic-drm driver

Hi Sam, thanks for the feedback.

Le ven. 1 mars 2019 à 17:16, Sam Ravnborg <sam@...nborg.org> a écrit :
> Hi Paul.
> 
> Good to see work migrating fbdev => drm.
> 
> Following comments is based on experience while working on migrating
> another driver from fbdev => drm.
> 
> On Thu, Feb 28, 2019 at 07:07:54PM -0300, Paul Cercueil wrote:
>>  Add documentation for the devicetree bindings of the DRM driver for 
>> the
>>  JZ47xx family of SoCs from Ingenic.
>> 
>>  Signed-off-by: Paul Cercueil <paul@...pouillou.net>
>>  Tested-by: Artur Rojek <contact@...ur-rojek.eu>
>>  ---
>>   .../devicetree/bindings/display/ingenic,drm.txt    | 30 
>> ++++++++++++++++++++++
>>   1 file changed, 30 insertions(+)
>>   create mode 100644 
>> Documentation/devicetree/bindings/display/ingenic,drm.txt
>> 
>>  diff --git 
>> a/Documentation/devicetree/bindings/display/ingenic,drm.txt 
>> b/Documentation/devicetree/bindings/display/ingenic,drm.txt
>>  new file mode 100644
>>  index 000000000000..52a368ec35cd
>>  --- /dev/null
>>  +++ b/Documentation/devicetree/bindings/display/ingenic,drm.txt
>>  @@ -0,0 +1,30 @@
>>  +Ingenic JZ47xx DRM driver
>>  +
>>  +Required properties:
>>  +- compatible: one of:
>>  +  * ingenic,jz4740-drm
>>  +  * ingenic,jz4725b-drm
>>  +- reg: LCD registers location and length
> The fbdev way of doing this was to hardcode register setttings.
> In the drm world we read the configuration of the panel and let
> this decide the actual configuration.
> 
> Note that no drm drivers supports stn displays and that there
> is really no use for this these days. So you can skip the STN parts.

STN panels aren't really my problem; but I have a board with a Sharp
LS020B1DD01D panel, which requires the LCD IP to be configured for a
"special 2" panel. I also have a board with a "smart" panel (ili9331)
that needs a special configuration in the IP. There is nothing in
the drm_panel interface that tells me what mode I should use for what
panel...

> Also the modern way to specify a panel in the DT is using OF graph 
> bindings.
> You can find many examples how to do this.

Ok, I was looking at the Tegra driver, which uses a "nvidia,panel" DT
property. I will change it to use the graph thing.

> I was there with the atmel LCDC driver (not in the kernel yet),
> and had some challenges with this.
> 
> 	Sam

Thanks,
-Paul

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