linux-kernel - Re: [PATCH 1/1] Support LVDS output on Allwinner A20

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Message-ID: <20200213092433.sc2rs7el63mwvf3y@gilmour.lan>
Date:   Thu, 13 Feb 2020 10:24:33 +0100
From:   Maxime Ripard <maxime@...no.tech>
To:     Andrey Lebedev <andrey.lebedev@...il.com>
Cc:     wens@...e.org, airlied@...ux.ie, daniel@...ll.ch,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] Support LVDS output on Allwinner A20

On Thu, Feb 13, 2020 at 12:46:53AM +0200, Andrey Lebedev wrote:
> On Wed, Feb 12, 2020 at 01:53:45PM +0100, Maxime Ripard wrote:
> > > > Side question, this will need some DT changes too, right?
> > >
> > > Hm, I agree. I think it would be reasonable to include LVDS0/1 pins
> >
> > That, but most importantly, the reset and clocks for the LVDS
> > block. Also from looking at it, I'm not entirely sure that the TCON1
> > has a LVDS output
>
> I also have impression that LVDS is only supported on TCON0, but that's
> mostly from this comment in sun4i_lvds.c:
>
> 	/* The LVDS encoder can only work with the TCON channel 0 */

No, that's a separate thing.

Internally the TCON has two channels, one connected to panels type of
display (LVDS, Parallel, etc), the second one connected to TV outputs
(HDMI, composite).

But then, on some SoCs like the A20, you have two TCON's too. As far
as I could see, only the first TCON can use LVDS, but I'm not
definitive.

Allwinner seems to allow panels to only be tied to TCON0 in the BSP,
so I guess we can assume that.

> > do you have a board when you have been able to test it?
>
> Yes, I have the hardware (Cubieboard 2) at hand, but I cannot change the
> any physical connections on it. FWIW, it is https://openvario.org, the
> device we are (painfully) trying to upgrade from old kernel-3.4 with
> proprietary mali drivers to contemporary software.

What painpoints do you have?

> > > and sample (but disabled) lvds panel,
> >
> > That's good for the sake of the example, but it shouldn't be in the
> > same patch, it won't be merged.
>
> I jave just submitted version 2 of the patches - set of 2 patches this
> time. Addressed your comments, please take a look.

I will, thanks!
Maxime

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