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From:   Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To:     Philippe CORNU <philippe.cornu@st.com>
Cc:     Mark Rutland <mark.rutland@arm.com>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        Alexandre TORGUE <alexandre.torgue@st.com>,
        David Airlie <airlied@linux.ie>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>,
        Yannick FERTRE <yannick.fertre@st.com>,
        Rob Herring <robh+dt@kernel.org>
Subject: Re: [PATCH 1/2] dt-bindings/display/bridge: sii902x: add optional power supplies
Date:   Thu, 19 Apr 2018 15:50:26 +0300
Message-ID: <5933919.oNossTj3O6@avalon>
Organization: Ideas on Board Oy
In-Reply-To: <a10d41bc-c766-568b-a9cb-d1f0f03390a8@st.com>
References: <20180410051927.8268-1-philippe.cornu@st.com> <1733412.i2Wslp7VkI@avalon> <a10d41bc-c766-568b-a9cb-d1f0f03390a8@st.com>
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Hi Philippe,

On Thursday, 19 April 2018 15:41:20 EEST Philippe CORNU wrote:
> On 04/19/2018 01:09 PM, Laurent Pinchart wrote:
> > 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@st.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.

I have seen that too. While the datasheet only says that the two supplies 
*can* be derived from the same power source, I expect that to be the case in 
practice for a really vast majority of cases (I wouldn't be surprised to never 
hear of a system using two different supplies). That's why I think starting 
with one supply would be better.

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

-- 
Regards,

Laurent Pinchart