[PATCH] imx-drm: imx-hdmi: fix hdmi hotplug detection initial state

[Fabio Estevam]

On Mon, Jun 9, 2014 at 11:06 AM, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:

> Please check the status in /sys/class/drm/card0-HDMI-A-1/status.  This
> should report the current state of the hotplug detection.

/sys/class/drm/card0-HDMI-A-1/status returns the correct state for
HDMI cable connection.

> Remember that this code detects off the HPD signal - if the HPD signal
> has not been correctly wired up, this patch is not going to help (really
> it comes down to a hardware fault, which I'm not trying to solve with
> this patch.)
>
> What I'm trying to resolve with this patch is that the state detected
> on properly wired up systems corresponds with the real initial state of
> the interface at initialisation time.
>
> The problem with the current code is that we start off assuming that the
> interface is disconnected, and we rely on an interrupt arriving to change
> that state.  If for whatever reason that interrupt does not arrive, then,
> even if the HPD signal is active, we continue believing that the interface
> is not connected.
>
> I seem to remember discussion in the past that the HPD signal is not
> wired up on SabreSD.  Really, this needs to be a DT flag to indicate

It is sabrelite board that does not have HPD signal not wired up.

sabresd does have HPD signal connected.

The HDMI undetected issue I am seeing on sabresd seems to be related
to the simultaneous usage of HDMI and LVDS.

If I remove the ldb node from the imx6qdl-sabresd.dtsi, then the HDMI
cable is correctly detected and HDMI is shown right after boot.