linux-kernel - Re: [PATCH v8 2/2] drm: bridge: Add thc63lvd1024 LVDS decoder driver

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Message-ID: <20180419123355.GB4235@w540>
Date:   Thu, 19 Apr 2018 14:33:55 +0200
From:   jacopo mondi <jacopo@...ndi.org>
To:     Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
Cc:     Jacopo Mondi <jacopo+renesas@...ndi.org>, architt@...eaurora.org,
        a.hajda@...sung.com, 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 v8 2/2] drm: bridge: Add thc63lvd1024 LVDS decoder driver

Hi Vladimir,

On Thu, Apr 19, 2018 at 02:18:30PM +0300, Vladimir Zapolskiy wrote:
> Hi Jacopo,
>
> On 04/10/2018 01:53 PM, Jacopo Mondi wrote:
> > Add DRM bridge driver for Thine THC63LVD1024 LVDS to digital parallel
> > output converter.
> >
> > Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
> > Reviewed-by: Andrzej Hajda <a.hajda@...sung.com>
> > Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>
>
> Reviewed-by: Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
>

Thanks. FYI I sent v9 yesterday with a minimal change compared to v8.

> Generally I have only one pretty ignorable comment.
>
> > +
> > +enum thc63_ports {
> > +	THC63_LVDS_IN0,
> > +	THC63_LVDS_IN1,
> > +	THC63_RGB_OUT0,
> > +	THC63_RGB_OUT1,
> > +};
> > +
>
> The driver uses only THC63_RGB_OUT0 value, or port@2, and MODE{0,1,2} IC
> configuration is ignored.
>
> I don't know if right from the beginning it would be better to support
> dual-out modes, preferably both single-in and dual-in ones. Will it
> impact port enumeration?

The bindings have been designed to support dual in/out modes, as you
can see there are 4 possible ports described there:

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

Future extension should not require changing the port enumeration,
just add a property to specify the selected mode.

>
> I do understand that the extension is possible, and likely only hardware
> accessibility postpones it.

Yes, hardware on one side, but also what I think is a shortcoming of
DRM (which exists in other sub-systems, say v4l2) that matches devices
on their OF device nodes and makes cumbersome handling drivers wanting
to register on 'port' nodes instead, as it would happen if you have 2
input endpoints.

See my [1] note here: https://lkml.org/lkml/2018/3/9/422
And this reply to Archit's comment which has been left floating as it
is not a real issue (yet): https://lkml.org/lkml/2018/3/10/214

Thanks
   j

>
> --
> With best wishes,
> Vladimir

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