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

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Message-ID: <a10d41bc-c766-568b-a9cb-d1f0f03390a8@st.com>
Date:   Thu, 19 Apr 2018 12:41:20 +0000
From:   Philippe CORNU <philippe.cornu@...com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
CC:     Mark Rutland <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        David Airlie <airlied@...ux.ie>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Yannick FERTRE <yannick.fertre@...com>,
        Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH 1/2] dt-bindings/display/bridge: sii902x: add optional
 power supplies

Hi Laurent,


On 04/19/2018 01:09 PM, Laurent Pinchart wrote:
> Hi Philippe,
> 
> On Thursday, 19 April 2018 12:31:15 EEST Philippe CORNU wrote:
>> On 04/19/2018 10:11 AM, Laurent Pinchart wrote:
>>> On Tuesday, 10 April 2018 08:19:26 EEST Philippe Cornu wrote:
>>>
>>>> Add the 3 optional power supplies using the exact description
>>>> found in the document named
>>>> "SiI9022A/SiI9024A HDMI Transmitter Data Sheet (August 2016)".
>>>>
>>>> Signed-off-by: Philippe Cornu <philippe.cornu@...com>
>>>> ---
>>>>
>>>>    Documentation/devicetree/bindings/display/bridge/sii902x.txt | 3 +++
>>>>    1 file changed, 3 insertions(+)
>>>>
>>>> diff --git
>>>> a/Documentation/devicetree/bindings/display/bridge/sii902x.txt
>>>> b/Documentation/devicetree/bindings/display/bridge/sii902x.txt index
>>>> 56a3e68ccb80..cf53678fe574 100644
>>>> --- a/Documentation/devicetree/bindings/display/bridge/sii902x.txt
>>>> +++ b/Documentation/devicetree/bindings/display/bridge/sii902x.txt
>>>> @@ -8,6 +8,9 @@ Optional properties:
>>>>    	- interrupts-extended or interrupt-parent + interrupts: describe
>>>>    	  the interrupt line used to inform the host about hotplug events.
>>>>    	- reset-gpios: OF device-tree gpio specification for RST_N pin.
>>>> +	- iovcc-supply: I/O supply voltage (1.8V or 3.3V, host-dependent).
>>>> +	- avcc12-supply: TMDS analog supply voltage (1.2V).
>>>> +	- cvcc12-supply: Digital core supply voltage (1.2V).
>>>
>>> It seems that the AVCC12 and CVCC12 power supplies are usually derived
>>> from the same source. How about starting with one DT property for both,
>>> and adding a second one later if needed ?
>>
>> Well, I do not know what is the best. Here I took the description from
>> the documentation, and to allow all possible board configurations, I
>> added these supplies as "optional" properties: if there is only one 1v2
>> regulator on the board, the dt will contain only avcc12 or cvcc12 and
>> everything will work fine (we will have a dummy regulator for the
>> missing optional 1v2 reg), if both regulators are there for any reasons
>> (stability, noise, whatever...) then both entries will be in the dt.
>>
>> If you confirm you prefer a single 1v2 supply (named for instance
>> "vcc12-supply") then I will do :-)
> 
> Please see https://lists.freedesktop.org/archives/dri-devel/2018-April/
> 172400.html (and the messages that lead to it) and https://
> lists.freedesktop.org/archives/dri-devel/2018-March/170763.html.
> 

Thanks for this discussion thread.

On my side, I found "CVCC12 and AVCC12 can be derived from the same 
power source" written with a small font (august 2016 datasheet p13) so 
then your advice is clearly what we have to do :-)
I will add this info in v2 too.
Thank you,
Philippe :-)

>>>>    Optional subnodes:
>>>>    	- video input: this subnode can contain a video input port node
>