linux-kernel - Re: [PATCH 2/3] dt-bindings: display: bridge: lvds-transmitter: add pwdn-gpios

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Message-ID: <4d5ca987-fdf4-6ebb-281f-29a8f3277329@axentia.se>
Date:   Wed, 19 Dec 2018 12:54:12 +0000
From:   Peter Rosin <peda@...ntia.se>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
CC:     Andrzej Hajda <a.hajda@...sung.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        David Airlie <airlied@...ux.ie>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Archit Taneja <architt@...eaurora.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH 2/3] dt-bindings: display: bridge: lvds-transmitter: add
 pwdn-gpios

On 2018-12-19 12:38, Laurent Pinchart wrote:
> Hello,
> 
> On Wednesday, 19 December 2018 11:57:32 EET Peter Rosin wrote:
>> On 2018-12-19 10:12, Andrzej Hajda wrote:
>>> On 19.12.2018 00:19, Peter Rosin wrote:
>>>> Add optional property to specify a power-down GPIO.
>>>> The pwdn-gpios name is already in use by the thine,thc63lvdm83d
>>>> binding, so go with that.
>>>>
>>>> Signed-off-by: Peter Rosin <peda@...ntia.se>
>>>> ---
>>>>
>>>>  Documentation/devicetree/bindings/display/bridge/lvds-transmitter.txt |
>>>>  3 +++ 
>>>>  1 file changed, 3 insertions(+)
>>>>
>>>> diff --git
>>>> a/Documentation/devicetree/bindings/display/bridge/lvds-transmitter.txt
>>>> b/Documentation/devicetree/bindings/display/bridge/lvds-transmitter.txt
>>>> index f9e7dd666f58..47941d39f92f 100644
>>>> ---
>>>> a/Documentation/devicetree/bindings/display/bridge/lvds-transmitter.txt
>>>> +++
>>>> b/Documentation/devicetree/bindings/display/bridge/lvds-transmitter.txt
>>>> @@ -31,6 +31,9 @@ Required properties:
>>>>    device-specific version corresponding to the device first
>>>>    followed by the generic version.
>>>>
>>>> +Optional properties:
>>>> +- pwdn-gpios: Power-down control GPIO
>>>> +
>>>
>>> Since naming is not enforced by any datasheet I would propose something
>>> more popular with less twisted logic. Maybe:
>>>
>>> - enable-gpios: ... (active high).
>>
>> That was my original thought too, but the driver implementing the
>> lvds-encoder bindings also handles the mentioned thine,thc63lvdm83d
>> lvds encoder, and that binding has the "pwdn" naming. So, for driver
>> implementation simplicity I went with what was already there, thus
>> allowing adding support for both bindings with one implementation
>> (in patch 3/3).
>>
>> Adding code just to handle multiple names for the same thing does
>> not sounds too appealing.
> 
> I'm afraid I think we shouldn't add pwdn-gpios support to the lvds encoder DT 
> bindings. The reason is that control GPIOs (and regulators) come with device-
> specific semantics. If we add pwdn-gpios now, we'll then add reset-gpios, and 
> power supplies, and all of a sudden we'll end up having to encode sequencing 
> of GPIOs and power supplies in DT. That path has been tried in the past, with 
> no good results.
> 
> I would instead create device-specific bindings, like done for 
> thine,thc63lvdm83d. It's fine to then add support for the pwdn-gpios property 
> in the lvds-encoder driver, as long as the meaning of the property comes from 
> specific DT bindings, not from the generic ones.

Right, I'll fork out the bindings for the texas chips. v2 coming up.

Cheers,
Peter