linux-kernel - Re: [PATCH v3 1/3] dt-bindings: display: bridge: Document THC63LVD1024 LVDS decoder

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Date:   Wed, 14 Mar 2018 10:06:51 +0100
From:   jacopo mondi <jacopo@...ndi.org>
To:     Andrzej Hajda <a.hajda@...sung.com>
Cc:     Jacopo Mondi <jacopo+renesas@...ndi.org>, architt@...eaurora.org,
        Laurent.pinchart@...asonboard.com, airlied@...ux.ie,
        horms@...ge.net.au, magnus.damm@...il.com, geert@...ux-m68k.org,
        niklas.soderlund@...natech.se, sergei.shtylyov@...entembedded.com,
        robh+dt@...nel.org, mark.rutland@....com,
        dri-devel@...ts.freedesktop.org, linux-renesas-soc@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] dt-bindings: display: bridge: Document
 THC63LVD1024 LVDS decoder

Hi Andrzej,
    sorry for the mess :(

On Wed, Mar 14, 2018 at 09:15:42AM +0100, Andrzej Hajda wrote:
> On 13.03.2018 15:30, Jacopo Mondi wrote:
> > Document Thine THC63LVD1024 LVDS decoder device tree bindings.
> >
> > Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
> > ---
> >  .../bindings/display/bridge/thine,thc63lvd1024.txt | 63 ++++++++++++++++++++++
> >  1 file changed, 63 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/display/bridge/thine,thc63lvd1024.txt
> >
> > diff --git a/Documentation/devicetree/bindings/display/bridge/thine,thc63lvd1024.txt b/Documentation/devicetree/bindings/display/bridge/thine,thc63lvd1024.txt
> > new file mode 100644
> > index 0000000..5b5afcd
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/display/bridge/thine,thc63lvd1024.txt
> > @@ -0,0 +1,63 @@
> > +Thine Electronics THC63LVD1024 LVDS decoder
> > +-------------------------------------------
> > +
> > +The THC63LVD1024 is a dual link LVDS receiver designed to convert LVDS streams
> > +to parallel data outputs. The chip supports single/dual input/output modes,
> > +handling up to two two input LVDS stream and up to two digital CMOS/TTL outputs.
> > +
> > +Required properties:
> > +- compatible: Shall be "thine,thc63lvd1024",
> > +
> > +Optional properties:
> > +- vcc-supply: Power supply for TTL output and digital circuitry
> > +- cvcc-supply: Power supply for TTL CLOCKOUT signal
> > +- lvcc-supply: Power supply for LVDS inputs
> > +- pvcc-supply: Power supply for PLL circuitry
>
> I wonder if it wouldn't be better to make them required (at least VCC) -
> it is closer to reality.

In cases like our Eagle board, where VCC is directly connected to the
powering rail and not through a controllable regulator, I feel like
making this mandatory requires more effort (not much, I agree, just a
"fixed-regulator" more) with no additional benefits.

But I understand your point, and I'm open to whatever fits better with
the already existing DRM bridges bindings

>
> > +- pwnd-gpios: Power down GPIO signal. Active low.
>
> As I said before, specs[1] says about "/PDWN" pin. Is it your typo, or
> different docs?

I didn't notice the typo in first review, and I thought you were referring to
the initial '/' which I found weird to be part of the gpio name... Then I now
realized I badly typed in "pwnd" in place of "pwdn", which is not even correct
because it has to be "pdwn"... Sorry about this mess, I will fix in v4

> Moreover there are already bindings for THC63LVDM83D with the same
> dichotomy [2].

Seems like this is 'wrong' as well.. The chip manual says the pin is
named "pdwn" here too..

>
> Out of curiosity I have googled for "pwnd pin" and it looks like some
> vendors use this form.
> For me both forms are quite misleading: power down signal, active low,
> why they couldn't call it just 'enable, active high'.
>

It's not much the actual physical active level that bugs me, but the fact
that the GPIO name defines if it has to be set to "active" or
"inactive" logical state in enable/disable routines that I don't
like..

> [1]: http://www.thine.co.jp/files/topics/179_ext_12_0.pdf
> [2]:
> https://elixir.bootlin.com/linux/v4.16-rc5/source/Documentation/devicetree/bindings/display/bridge/thine,thc63lvdm83d.txt
>
> > +- oe-gpios: Output enable GPIO signal. Active high.
> > +
> > +The THC63LVD1024 video port connections are modeled according
> > +to OF graph bindings specified by Documentation/devicetree/bindings/graph.txt
> > +
> > +Required video port nodes:
> > +- Port@0: First LVDS input port
> > +- Port@2: First digital CMOS/TTL parallel output
> > +
> > +Optional video port nodes:
> > +- Port@1: Second LVDS input port
> > +- Port@3: Second digital CMOS/TTL parallel output
> > +
> > +Example:
> > +--------
> > +
> > +	thc63lvd1024: lvds-decoder {
> > +		compatible = "thine,thc63lvd1024";
> > +
> > +		vcc-supply = <&reg_lvds_vcc>;
> > +		lvcc-supply = <&reg_lvds_lvcc>;
> > +
> > +		pwdn-gpio = <&gpio4 15 GPIO_ACTIVE_LOW>;
> And here another variation :), should be pdwn-gpios.

Next time it will be "pndw".. Is there a prize if I do insert all
permutations of the same name in a single bindings document? :)

Will fix this shortly.

Thanks
   j

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