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Subject: Re: [PATCH 2/3] dt-bindings: new binding for Ilitek ILI9341 display
 panels
To:     =?UTF-8?Q?Noralf_Tr=c3=b8nnes?= <noralf@tronnes.org>,
        dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org
Cc:     Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>, limor@ladyada.net,
        Nitin Patil <nitin@mindsensors.com>,
        linux-kernel@vger.kernel.org
References: <20180515014349.26226-1-david@lechnology.com>
 <20180515014349.26226-3-david@lechnology.com>
 <50928486-822a-aff3-7c37-cc1c40cb62b8@tronnes.org>
From:   David Lechner <david@lechnology.com>
Message-ID: <b86e0eac-35bb-e143-ad44-8a091af798a5@lechnology.com>
Date:   Sat, 19 May 2018 10:50:17 -0500
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On 05/19/2018 08:37 AM, Noralf Trønnes wrote:
> 
> Den 15.05.2018 03.43, skrev David Lechner:
>> This adds a new binding for Ilitek ILI9341 display panels. It includes
>> a compatible string for one display (more can be added in the future).
>>
>> The vendor prefix "noname" is used because the vendor is not known.
>> The YX240QV29-T panel[1] is found, for example, in an Adafruit breakout
>> board[2] and in Mindsensors' PiStorms[3].
>>
>> [1]: https://cdn-learn.adafruit.com/assets/assets/000/046/879/original/SPEC-YX240QV29-T_Rev.A__1_.pdf
>> [2]: https://www.adafruit.com/product/2478
>> [3]: http://www.mindsensors.com/stem-with-robotics/13-pistorms-v2-base-kit-raspberry-pi-brain-for-lego-robot
>>
>> Signed-off-by: David Lechner <david@lechnology.com>
>> ---
>>   .../bindings/display/ilitek,ili9341.txt       | 27 +++++++++++++++++++
>>   1 file changed, 27 insertions(+)
>>   create mode 100644 Documentation/devicetree/bindings/display/ilitek,ili9341.txt
>>
>> diff --git a/Documentation/devicetree/bindings/display/ilitek,ili9341.txt b/Documentation/devicetree/bindings/display/ilitek,ili9341.txt
>> new file mode 100644
>> index 000000000000..0fc90b2dd732
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/display/ilitek,ili9341.txt
>> @@ -0,0 +1,27 @@
>> +Ilitek ILI9341 display panels
>> +
>> +This binding is for display panels using an Ilitek ILI9341 controller in SPI
>> +mode.
>> +
>> +Required properties:
>> +- compatible:    "noname,yx240qv29", "ilitek,ili9341"
> 
> Calling a vendor 'noname' looks a bit odd and AFAICT it isn't used by
> any other binding. A google search always mentions Adafruit in
> connection with this panel, so I suggest we use Adafruit as vendor.

I was hoping that someone might know the correct vendor, but barring that,
I agree that adafruit is probably the best choice.

> 
> I don't think we should use "ilitek,ili9341" as an option/fallback,
> because panels varies in resolution (rarely) and initialization. A
> generic ili9341 driver would probably not work with a random new panel.

I'm just following the precedent set in the other bindings for similar
displays that I have already done.

References:
* https://patchwork.freedesktop.org/patch/194648/
* https://patchwork.freedesktop.org/patch/195320/

I agree that it is probably not super-useful as a fallback. On the other
hand, the vendors and models for these displays are pretty obscure and
I think having the more well-known controller name _somewhere_ is useful.


> 
>> +- dc-gpios:    D/C pin
>> +- reset-gpios:    Reset pin
>> +
>> +The node for this driver must be a child node of a SPI controller, hence
>> +all mandatory properties described in ../spi/spi-bus.txt must be specified.
>> +
>> +Optional properties:
>> +- rotation:    panel rotation in degrees counter clockwise (0,90,180,270)
>> +- backlight:    phandle of the backlight device attached to the panel
> 
> You forgot to mention the regulator that you support in the driver.
> 
> Noralf.
> 
>> +
>> +Example:
>> +    display@0{
>> +        compatible = "noname,yx240qv29", "ilitek,ili9341";
>> +        reg = <0>;
>> +        spi-max-frequency = <32000000>;
>> +        dc-gpios = <&gpio0 9 GPIO_ACTIVE_HIGH>;
>> +        reset-gpios = <&gpio0 8 GPIO_ACTIVE_HIGH>;
>> +        rotation = <270>;
>> +        backlight = <&backlight>;
>> +    };
>