Fwd: [Intel-gfx] [PATCH 1/2] drm: give up on edid retries when i2c bus is not responding

[Eugeni Dodonov]

Looks like a CC to dri-devel got forgotten originally, so forwarding it
properly.

---------- Forwarded message ----------
From: Eugeni Dodonov <eugeni.dodonov at intel.com>
Date: Thu, Jan 5, 2012 at 09:34
Subject: [Intel-gfx] [PATCH 1/2] drm: give up on edid retries when i2c bus
is not responding
To: intel-gfx at lists.freedesktop.org
Cc: Eugeni Dodonov <eugeni.dodonov at intel.com>


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 at hchris-wilson.co.uk>
Reviewed-by: Keith Packard <keithp at keithp.com>
Tested-by: Sean Finney <seanius at seanius.net>
Tested-by: Soren Hansen <soren at linux2go.dk>
Tested-by: Hernando Torque <sirius at sonnenkinder.org>
Tested-by: Mike Lothian <mike at fireburn.co.uk>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=41059
Signed-off-by: Eugeni Dodonov <eugeni.dodonov at intel.com>
---
 drivers/gpu/drm/drm_edid.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 3e927ce..fb6c26c 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;
--
1.7.8

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-- 
Eugeni Dodonov
<http://eugeni.dodonov.net/>
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