linux-kernel - Re: [PATCH 1/2] drm: bridge/dw

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Message-ID: <20150807141346.GH7557@n2100.arm.linux.org.uk>
Date:	Fri, 7 Aug 2015 15:13:46 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Sascha Hauer <s.hauer@...gutronix.de>
Cc:	Thierry Reding <treding@...dia.com>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] drm: bridge/dw_hdmi: Cache edid data

On Fri, Aug 07, 2015 at 03:59:20PM +0200, Sascha Hauer wrote:
> Instead of rereading the edid data each time userspace asks for them
> read them once and cache them in the previously unused edid field in
> struct dw_hdmi. This makes the code a little bit more efficient.

How has this been tested?

Has it been tested with an AV amplifier in the path to the display device?
If not, it really needs to be tested, because such devices modify the EDID
data, or subsitute their own, and alter the EDID data depending on their
needs.  When they do, they lower and re-assert the HPD signal, possibly
for as little as 100ms - defined by the HDMI spec.

For example, an AV amplifier in standby can provide the displays EDID in
the first page of EDID, along with the displays extended EDID in the
second page.  When the AV amplifier is powered up, it can provide a
different second page of EDID information detailing the audio formats
that it can accept, and it will lower and re-assert the HPD signal to
cause the connected devices to read the updated EDID information.  Same
thing can happen when switching to standby mode too.

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