From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Philipp Zabel <p.zabel@pengutronix.de>
Cc: Thierry Reding <treding@nvidia.com>,
kernel@pengutronix.de, dri-devel@lists.freedesktop.org
Subject: Re: [PATCH 4/4] drm: bridge/dw-hdmi: use rx sense for plug detection if hpd is unreliable
Date: Fri, 8 Jan 2016 11:34:40 +0000 [thread overview]
Message-ID: <20160108113440.GI19062@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <1452243727-7242-4-git-send-email-p.zabel@pengutronix.de>
On Fri, Jan 08, 2016 at 10:02:07AM +0100, Philipp Zabel wrote:
> Due to the voltage divider on the HPD line, the HDMI connector on
> imx6q-sabrelite doesn't reliably detect connected DVI monitors.
> This patch allows to use the RX_SENSE signals as a workaround when
> enabled by a boolean device tree property 'hpd-unreliable'.
There's a got-cha here. On iMX6S, the RXSENSE interrupts bounce
around madly if the HDMI interface is not fully configured. I've
seen this many times at boot time (I've been carrying a patch which
reports the HPD/RXSENSE state to the kernel log for a long time now,
it can be rather noisy.)
It's also out-of-spec for reading the EDID: the EDID is only valid
when HPD is asserted. When HPD is deasserted, the EDID may not be
accessible. Using RXSENSE opens a window where the EDID may be
unavailable, or may be mid-way through being updated depending on
how the sink hardware works.
With a Yamaha RX-V677 AV receiver and a Panasonic TV, I've observed
this:
initial(-rxsense,-hpd), AV standby, TV standby.
Connected to AV: +rxsense, +hpd
EDID reads from AV
TV standby->on: -hpd, 2s, +hpd
EDID reads from TV
AV standby->on: -hpd, 1.2s, +hpd
EDID reads combined TV/AV
AV on->standby: -hpd, 1.2s, +hpd
EDID reads from TV
Note that RXSENSE did not drop, but the EDID changed, and that change
was properly signalled via HPD according to the HDMI standard.
--
RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.
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prev parent reply other threads:[~2016-01-08 11:34 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-08 9:02 [PATCH 1/4] drm: bridge/dw-hdmi: cache edid data Philipp Zabel
2016-01-08 9:02 ` [PATCH 2/4] drm: bridge/dw-hdmi: remove unused code Philipp Zabel
2016-01-08 9:02 ` [PATCH 3/4] drm: bridge/dw-hdmi: detect initial connector state Philipp Zabel
2016-01-08 11:24 ` Russell King - ARM Linux
2016-01-08 11:40 ` Philipp Zabel
2016-03-02 16:35 ` Thierry Reding
2016-01-08 9:02 ` [PATCH 4/4] drm: bridge/dw-hdmi: use rx sense for plug detection if hpd is unreliable Philipp Zabel
2016-01-08 11:34 ` Russell King - ARM Linux [this message]
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