From mboxrd@z Thu Jan  1 00:00:00 1970
From: Shawn Guo <shawn.guo@freescale.com>
Subject: Re: [PATCH] imx-drm: imx-hdmi: fix hdmi hotplug detection initial
 state
Date: Mon, 9 Jun 2014 22:33:16 +0800
Message-ID: <20140609143315.GA8860@dragon>
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To: Fabio Estevam <festevam@gmail.com>
Cc: devel@driverdev.osuosl.org, Russell King - ARM Linux <linux@arm.linux.org.uk>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Tim Harvey <tharvey@gateworks.com>, DRI mailing list <dri-devel@lists.freedesktop.org>, Philipp Zabel <philipp.zabel@gmail.com>
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On Mon, Jun 09, 2014 at 11:29:28AM -0300, Fabio Estevam wrote:
> On Mon, Jun 9, 2014 at 11:06 AM, Russell King - ARM Linux
> <linux@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.

This is a known limitation.

http://thread.gmane.org/gmane.linux.ports.arm.kernel/315968/focus=318559

Shawn