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

[Daniel Vetter]

Hi Dave,

Is it ok if I merge this through my -next tree? Otherwise please consider
merging this for 3.4.

Yours, Daniel

On Thu, Jan 05, 2012 at 09:34:28AM -0200, Eugeni Dodonov wrote:
> 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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-- 
Daniel Vetter
Mail: daniel at ffwll.ch
Mobile: +41 (0)79 365 57 48