linux-kernel - Re: [PATCH 0/7] drm/sun4i: Introduce A33 display driver

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Date:   Tue, 6 Sep 2016 20:54:52 +0200
From:   Maxime Ripard <maxime.ripard@...e-electrons.com>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Icenowy Zheng <icenowy@...c.xyz>,
        Daniel Vetter <daniel.vetter@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Thierry Reding <thierry.reding@...il.com>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-sunxi@...glegroups.com" <linux-sunxi@...glegroups.com>,
        Rob Herring <robh+dt@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 0/7] drm/sun4i: Introduce A33 display driver

On Tue, Sep 06, 2016 at 10:50:09AM +0800, Chen-Yu Tsai wrote:
> >> The implementation might be along the lines of
> >>
> >>   1. having multiple output ports, each for a different interface type.
> >>      (Some platforms go this route)
> >>
> >> Or
> >>
> >>   2. having a DT property describe what the output interface is.
> >>
> >> The RGB/TCON driver would then setup the registers accordingly.
> >
> > Hmmm, yeah, we would need to adjust the bindings too...
> >
> > I guess I'd prefer 1), but that would also be the most invasive
> > solution. I'm not sure how the DT maintainers feel about that.
> 
> I wonder if the TCON could use its 2 channels simultaneously?

No, it's mutually exclusive.

> Like output to one LCD, then mirror through HDMI/VGA?
> The first option would be able to cover this better?

Even if it wasn't exclusive, that wouldn't be possible
unfortunately. Or rather, this would be possible if the LCD and the
HDMI screen had the same timings, which is very unlikely.

> And you still need to add outgoing endpoints for the HDMI block.

Indeed.

> In addition we'll have to rework the TV encoder binding as well.
> 
> The 2 TV encoders (on the A20) each have four DACs, which map
> onto 4 external pins. The address space includes a not so easy
> to use mux. More importantly, the binding needs to specify which
> pin is used for what signal (RGB, YUV, S/Video, composite).
> There seems to be an implicit rule that 1 pin is always used
> for composite, and the 3 others RGB, though.

I'm not sure why we would need to rework this one though. We have no
way to detect whether the screen is connected or not on either
connectors, and we can't have both output running at the same time for
the same reason than mention above.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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