linux-kernel - Re: [PATCH 1/3] dt-bindings: display: bridge: Document THC63LVD1024 LVDS decoder

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Date:   Fri, 9 Mar 2018 10:22:39 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     jacopo mondi <jacopo@...ndi.org>
Cc:     Jacopo Mondi <jacopo+renesas@...ndi.org>,
        Archit Taneja <architt@...eaurora.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        David Airlie <airlied@...ux.ie>,
        Simon Horman <horms@...ge.net.au>,
        Magnus Damm <magnus.damm@...il.com>,
        Niklas Söderlund <niklas.soderlund@...natech.se>,
        Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] dt-bindings: display: bridge: Document THC63LVD1024
 LVDS decoder

Hi Jacopo,

On Fri, Mar 9, 2018 at 10:04 AM, jacopo mondi <jacopo@...ndi.org> wrote:
> On Fri, Mar 09, 2018 at 09:10:55AM +0100, Geert Uytterhoeven wrote:
>> On Thu, Mar 8, 2018 at 4:24 PM, Jacopo Mondi <jacopo+renesas@...ndi.org> wrote:
>> > Document Thine THC63LVD1024 LVDS decoder.
>> >
>> > Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
>>
>> Thanks for your patch!
>>
>> > --- /dev/null
>> > +++ b/Documentation/devicetree/bindings/display/bridge/thine,thc63lvd1024.txt
>> > @@ -0,0 +1,59 @@
>> > +THine Electronics THC63LVD1024 LVDS receiver
>>
>> Thine
>>
>> > +--------------------------------------------
>> > +
>> > +The THC63LVD1024 is an LVDS receiver designed to convert multiple LVDS streams
>> > +to digital CMOS/TTL parallel data.
>> > +
>> > +Required properties:
>> > +- compatible: Shall be one of the following:
>> > +  "thine,thc63lvd1024",
>> > +  "lvds-decoder"
>>
>> What's the purpose of the second compatible value?
>> When should it be used?
>
> It is probably my bad having started with a generic LVDS decoder in
> mind and having then added properties specific to THC63LVD1024 to the
> driver and its bindings.
>
> "lvds,decoder" can be used when the chip is completely transparent to
> the SoC and none of the optional properties I have described in the
> bindings are specified (a generic "power-gpios" apart, see Andrzej
> comments on "pwdn-gpios" property).
>
> Also, I should make the driver behavior depend on the matched compatible
> string. When "lvds-decoder" is matched, it will just look for an
> optional power down gpio, when "thc63lvd1024" is matched, all of its
> Vcc supplies, pwdn gpio and oe gpios will be queried and, if present,
> eventually used in enable/disable routines.
>
> I'm just not sure how to describe that in bindings. Would something
> like the following work?
>
> Optional properties for "lvds,decoder"

"lvds-decoder"?

> - power-gpios: Power control GPIOs
>
> Optional properties for "thine,thc63lvd1024"
> - pwdn-gpios: ...
> - oe-gpios: ...
> - supply-vcc: ...
> - supply-cvcc: ...
> - supply-pvcc: ...
> - supply-lvcc: ...

Sounds like you need a (separate) generic lvds-decoder DT bindings document,
which you can extend/refer to from the THC63LVD1024-specific bindings.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds