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

[Chen-Yu Tsai <wens@csie.org>]

On Wed, Sep 7, 2016 at 2:54 AM, Maxime Ripard
<maxime.ripard@free-electrons.com> wrote:
> 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.

I don't see how though. Are you referring to the IO_Map_Sel bit?
I assume that only controls the external output pins though.

>> 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.

What about an LCD-VGA bridge + HDMI in mirror mode on sun6i?
That should work.

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

On second thought, this particular one shouldn't affect the binding.

>
>> 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.

I would like to add connector nodes. At least we can specify stuff
like what DAC outputs are used for which connector, what type of
connector, and a ddc bus for VGA connectors. I haven't worked out
the details though.

Regards
ChenYu