[linux-sunxi] Re: [PATCH 02/12] drm: sun4i: Add support for enabling DDC I2C bus to dw_hdmi glue

[Maxime Ripard]

On Mon, Apr 08, 2019 at 02:17:27PM +0200, Ondřej Jirman wrote:
> On Mon, Apr 08, 2019 at 10:47:14AM +0200, Maxime Ripard wrote:
> > On Mon, Apr 08, 2019 at 03:28:24PM +0800, Chen-Yu Tsai wrote:
> > > On Mon, Apr 8, 2019 at 3:23 PM Maxime Ripard <maxime.ripard at bootlin.com> wrote:
> > > >
> > > > On Sat, Apr 06, 2019 at 01:45:04AM +0200, megous at megous.com wrote:
> > > > > From: Ondrej Jirman <megous at megous.com>
> > > > >
> > > > > Orange Pi 3 board requires enabling DDC I2C bus via some GPIO connected
> > > > > transistors, before it can be used. Model this as a power supply for DDC
> > > > > (via regulator framework).
> > > > >
> > > > > Signed-off-by: Ondrej Jirman <megous at megous.com>
> > > >
> > > > The DDC bus itself is usually attached to the HDMI connector, so it
> > > > would make sense to make the supply also a property of the connector.
> > >
> > > I believe these are separate things. What this patch covers is power for
> > > a voltage shifter between the SoC and HDMI DDC pins. The HDMI connector's
> > > 5V supply to power the remote DDC chip is something else. And on the
> > > Orange Pi 3 they are indeed separate supplies.
> >
> > Then maybe the endpoint link between the two would be the best place
> > to put this?
>
> Interestingly &hdmi node configures the DDC bus pins via pinctrl on the SoC
> side, so I put this there too, because it's related to those pins. I'm not sure
> if that changes anything in the discussion.

It's kind of different though. The DDC controller is within the HDMI
controller, which is inside the SoC. Just like the pin muxer. As far
as the hardware goes, even on your board, you don't need that supply
so that the signal gets out of the SoC.

If the regulator is to power up some component on the path between the
SoC and the connector, then it should be attached there.

Maxime

--
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
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