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

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Date:   Fri, 9 Mar 2018 10:04:22 +0100
From:   jacopo mondi <jacopo@...ndi.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.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 Geert,
   thanks for review

On Fri, Mar 09, 2018 at 09:10:55AM +0100, Geert Uytterhoeven wrote:
> Hi Jacopo,
>
> 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"
- power-gpios: Power control GPIOs

Optional properties for "thine,thc63lvd1024"
- pwdn-gpios: ...
- oe-gpios: ...
- supply-vcc: ...
- supply-cvcc: ...
- supply-pvcc: ...
- supply-lvcc: ...

Thanks
   j

>
> 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