Re: [PATCH v3 3/6] dt-bindings: add binding for Sitronix ST7586 display panels

From: "Noralf Trønnes" <noralf@tronnes.org>
To: David Lechner <david@lechnology.com>,
	dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org
Cc: Daniel Vetter <daniel@ffwll.ch>, David Airlie <airlied@linux.ie>,
	Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>, Sekhar Nori <nsekhar@ti.com>,
	Kevin Hilman <khilman@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 3/6] dt-bindings: add binding for Sitronix ST7586 display panels
Date: Fri, 4 Aug 2017 20:04:25 +0200	[thread overview]
Message-ID: <20c044a4-cefe-7fed-8c5d-af27829c0648@tronnes.org> (raw)
In-Reply-To: <e824aca6-b668-1d63-65a0-c56bfd8bec79@lechnology.com>

Den 04.08.2017 18.51, skrev David Lechner:
> On 08/04/2017 04:48 AM, Noralf Trønnes wrote:
>>
>> Den 04.08.2017 00.33, skrev David Lechner:
>>> This adds a new binding for Sitronix ST7586 display panels.
>>>
>>> Using lego as the vendor prefix in the compatible string because the 
>>> display
>>> panel I am working with is an integral part of the LEGO MINDSTORMS EV3.
>>
>> Is this display available outside of this Lego part?
> No, it is not.
>
>> If not you can remove the properties you don't need for this particular
>> display setup. Another st7586 display with a different panel would need
>> a different initialization sequence and compatible string, so we can
>> add properties when/if that happens.
>
> OK. so I will drop power-supply and backlight.
>

And the dc/reset gpios should be required properties since your display
won't work without them (or rather they're hardwired that way).

> Should I remove these from the driver as well? There are some panels 
> out there that could use them.[1]
>
> [1]: 
> http://www.buydisplay.com/download/manual/ERC240160-1_Series_Datasheet.pdf
>

Yes, because that display won't work with the driver as-is, so it's
really dead code. If someone wants to add support for that display,
they'll add the necessary code. When maintaining code for 10-20 years,
it's important to not add code that 'might' be used in the future.
Let the future take care of itself and keep the codebase slim :-)

Noralf.

>>
>> Noralf.
>>
>>> Signed-off-by: David Lechner <david@lechnology.com>
>>> ---
>>>   .../bindings/display/sitronix,st7586.txt           | 26 
>>> ++++++++++++++++++++++
>>>   1 file changed, 26 insertions(+)
>>>   create mode 100644 
>>> Documentation/devicetree/bindings/display/sitronix,st7586.txt
>>>
>>> diff --git 
>>> a/Documentation/devicetree/bindings/display/sitronix,st7586.txt 
>>> b/Documentation/devicetree/bindings/display/sitronix,st7586.txt
>>> new file mode 100644
>>> index 0000000..dfb0b7b
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/display/sitronix,st7586.txt
>>> @@ -0,0 +1,26 @@
>>> +Sitronix ST7586 display panel
>>> +
>>> +Required properties:
>>> +- compatible:    "lego,ev3-lcd".
>>> +
>>> +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:
>>> +- dc-gpios:    D/C pin. The presence/absence of this GPIO determines
>>> +        the panel interface operation mode (IF[3:1] pins):
>>> +        - present: IF=011 4-wire 8-bit data serial interface
>>> +        - absent:  IF=010 3-wire 9-bit data serial interface
>>> +- reset-gpios:    Reset pin
>>> +- power-supply:    A regulator node for the supply voltage.
>>> +- backlight:    phandle of the backlight device attached to the panel
>>> +- rotation:    panel rotation in degrees counter clockwise 
>>> (0,90,180,270)
>>> +
>>> +Example:
>>> +    display@0{
>>> +        compatible = "lego,ev3-lcd";
>>> +        reg = <0>;
>>> +        spi-max-frequency = <10000000>;
>>> +        dc-gpios = <&gpio 43 GPIO_ACTIVE_HIGH>;
>>> +        reset-gpios = <&gpio 80 GPIO_ACTIVE_HIGH>;
>>> +    };
>>
>