Re: [PATCH v2 1/2] dt-bindings/display/bridge: sii902x: add optional power supplies

[Philippe CORNU <philippe.cornu@st.com>]

Hi Rob & Laurent :)

On 04/26/2018 12:05 AM, Laurent Pinchart wrote:
> Hi Rob,
> 
> On Wednesday, 25 April 2018 20:11:23 EEST Rob Herring wrote:
>> On Wed, Apr 25, 2018 at 04:17:25PM +0300, Laurent Pinchart wrote:
>>> On Wednesday, 25 April 2018 15:20:04 EEST Philippe CORNU wrote:
>>>> On 04/25/2018 11:01 AM, Laurent Pinchart wrote:
>>>>> On Wednesday, 25 April 2018 10:53:13 EEST Philippe Cornu wrote:
>>>>>> Add optional power supplies using the description found in
>>>>>> "SiI9022A/SiI9024A HDMI Transmitter Data Sheet (August 2016)".
>>>>>>
>>>>>> There is a single 1v2 supply voltage named vcc12 from which cvcc12
>>>>>> (digital core) and avcc12 (TMDS analog) are derived because according
>>>>>> to this data sheet:
>>>>>> "cvcc12 and avcc12 can be derived from the same power source"
>>>>>
>>>>> Shouldn't the power supplies be mandatory, as explained by Mark in
>>>>> https://lists.freedesktop.org/archives/dri-devel/2018-April/172400.html
>>>>> ?
>>>>
>>>> Laurent,
>>>> Many thanks Laurent for your comment, I understood the merge of the two
>>>> 1v2 power supplies but missed the "mandatory" part... maybe because this
>>>> patch (with optional power supplies) already got the reviewed-by from
>>>> Rob, I thought the discussion thread you pointed out was applicable
>>>> "only" to totally new driver documentation.
>>>>
>>>> So, on my side, as a "new user" of sii902x IC, no problem to put these
>>>> power supplies as mandatory instead of optional properties but I would
>>>> like to be sure this is applicable to both old and new bindings doc : )
>>>
>>> We obviously need to retain backward compatibility, so on the driver side
>>> you need to treat those power supplies as optional. From a DT bindings
>>> point of view, however, I think they should be mandatory for new DT.
>>
>> We don't really have a way to describe these 3 conditions (required for
>> all, optional for all, and required for new). So generally we make
>> additions optional. The exception sometimes is if we update all the dts
>> files.
> 
> Can't we just make it mandatory in the bindings, as long as we treat it as
> optional in drivers ?
> 

How to progress on this patch? Do you have any suggestions?

Many thanks for your help,
Philippe :-)

>>>> Rob,
>>>> could you please confirm these power supply properties should be
>>>> "mandatory"? if yes, should we then modify other optional properties like
>>>> the reset-gpios too in the future?
>>>
>>> The GPIOs properties are different in my opinion, as there's no
>>> requirement to connect for instance the reset pin to a GPIO controllable
>>> by the SoC. The pin could be hardwired to VCC, or connected to a system
>>> reset that is automatically managed without SoC intervention. The power
>>> supplies, however, are mandatory, in the sense that the chip will not work
>>> if you leave the power supplies unconnected.
>>
>> DT only needs to describe what matters to s/w. If a regulator is
>> fixed and you don't need to know its voltage (or other read-only
>> parameters), then there's not much point in putting it in DT.
>>
>> I'd probably base this more at a platform level and you either use
>> regulator binding or you don't. It's perfectly valid that you want to do
>> things like regulator setup, pin ctrl and muxing setup, etc. all in
>> firmware and the OS doesn't touch any of that.
>>
>> That's all a big can of worms which we shouldn't solve on this 2 line
>> change. I think this change is fine as-is, so:
>>
>> Reviewed-by: Rob Herring <robh@kernel.org>
>