linux-kernel - Re: [PATCH 7/7] dt-bindings: display: add panel-timing property to sitronix,st7789v

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Date:   Thu, 16 Mar 2023 23:29:53 +0100
From:   Michael Riesch <michael.riesch@...fvision.net>
To:     Rob Herring <robh@...nel.org>,
        Gerald Loacker <gerald.loacker@...fvision.net>
Cc:     dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Thierry Reding <thierry.reding@...il.com>,
        Sam Ravnborg <sam@...nborg.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Maxime Ripard <mripard@...nel.org>
Subject: Re: [PATCH 7/7] dt-bindings: display: add panel-timing property to
 sitronix,st7789v

Hi Rob,

On 3/16/23 22:57, Rob Herring wrote:
> On Tue, Mar 14, 2023 at 12:56:44PM +0100, Gerald Loacker wrote:
>> The sitronix-st7789v driver now considers the panel-timing property.
> 
> I read the patch for that and still don't know 'why'. Commit messages 
> should answer why.
> 
>> Add the property to the documentation.
> 
> We generally don't put timings in DT for panels. Why is this one 
> special?

For now, having the timings in the device tree allows for setting the
hsync/vsync/de polarity.

As a next step, we aim to implement the partial mode feature of this
panel. It is possible to use only a certain region of the panel, which
is helpful e.g., when a part of the panel is occluded and should not be
considered by DRM. We thought that this could be specified as timing in DT.

(The hactive and vactive properties serve as dimensions of this certain
region, of course. We still need to specify somehow the position of the
region. Maybe with additional properties hactive-start and vactive-start?)

What do you think about that?

Thanks and best regards,
Michael

> 
>>
>> Signed-off-by: Gerald Loacker <gerald.loacker@...fvision.net>
>> ---
>>  .../display/panel/sitronix,st7789v.yaml         | 17 +++++++++++++++++
>>  1 file changed, 17 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml b/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml
>> index ed942cd3620f..8810f123dedf 100644
>> --- a/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml
>> +++ b/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml
>> @@ -21,6 +21,7 @@ properties:
>>    reset-gpios: true
>>    power-supply: true
>>    backlight: true
>> +  panel-timing: true
>>    port: true
>>    rotation: true
>>  
>> @@ -54,6 +55,22 @@ examples:
>>              spi-cpol;
>>              spi-cpha;
>>  
>> +            panel-timing {
>> +                clock-frequency = <7000000>;
>> +                hactive = <240>;
>> +                vactive = <320>;
>> +                hfront-porch = <38>;
>> +                hback-porch = <10>;
>> +                hsync-len = <10>;
>> +                vfront-porch = <8>;
>> +                vback-porch = <4>;
>> +                vsync-len = <4>;
>> +                hsync-active = <1>;
>> +                vsync-active = <1>;
>> +                de-active = <1>;
>> +                pixelclk-active = <1>;
>> +            };
>> +
>>              port {
>>                  panel_input: endpoint {
>>                      remote-endpoint = <&tcon0_out_panel>;
>> -- 
>> 2.37.2
>>