linux-kernel - [ 006/173] drm: give up on edid retries when i2c bus is not responding

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Message-Id: <20121228190331.341180069@decadent.org.uk>
Date:	Fri, 28 Dec 2012 20:03:36 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Eugeni Dodonov <eugeni.dodonov@...el.com>,
	Chris Wilson <chris@...ris-wilson.co.uk>,
	Keith Packard <keithp@...thp.com>,
	Sean Finney <seanius@...nius.net>,
	Soren Hansen <soren@...ux2go.dk>,
	Hernando Torque <sirius@...nenkinder.org>,
	Mike Lothian <mike@...eburn.co.uk>,
	Dave Airlie <airlied@...hat.com>
Subject: [ 006/173] drm: give up on edid retries when i2c bus is not responding

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eugeni Dodonov <eugeni.dodonov@...el.com>

commit 9292f37e1f5c79400254dca46f83313488093825 upstream.

This allows to avoid talking to a non-responding bus repeatedly until we
finally timeout after 15 attempts. We can do this by catching the -ENXIO
error, provided by i2c_algo_bit:bit_doAddress call.

Within the bit_doAddress we already try 3 times to get the edid data, so
if the routine tells us that bus is not responding, it is mostly pointless
to keep re-trying those attempts over and over again until we reach final
number of retries.

This change should fix https://bugs.freedesktop.org/show_bug.cgi?id=41059
and improve overall edid detection timing by 10-30% in most cases, and by
a much larger margin in case of phantom outputs (up to 30x in one worst
case).

Timing results for i915-powered machines for 'time xrandr' command:
Machine 1: from 0.840s to 0.290s
Machine 2: from 0.315s to 0.280s
Machine 3: from +/- 4s to 0.184s

Timing results for HD5770 with 'time xrandr' command:
Machine 4: from 3.210s to 1.060s

Reviewed-by: Chris Wilson <chris@...ris-wilson.co.uk>
Reviewed-by: Keith Packard <keithp@...thp.com>
Tested-by: Sean Finney <seanius@...nius.net>
Tested-by: Soren Hansen <soren@...ux2go.dk>
Tested-by: Hernando Torque <sirius@...nenkinder.org>
Tested-by: Mike Lothian <mike@...eburn.co.uk>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=41059
Signed-off-by: Eugeni Dodonov <eugeni.dodonov@...el.com>
Signed-off-by: Dave Airlie <airlied@...hat.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/gpu/drm/drm_edid.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index ece03fc..54a4efa 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -266,6 +266,11 @@ drm_do_probe_ddc_edid(struct i2c_adapter *adapter, unsigned char *buf,
 			}
 		};
 		ret = i2c_transfer(adapter, msgs, 2);
+		if (ret == -ENXIO) {
+			DRM_DEBUG_KMS("drm: skipping non-existent adapter %s\n",
+					adapter->name);
+			break;
+		}
 	} while (ret != 2 && --retries);
 
 	return ret == 2 ? 0 : -1;


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