linux-kernel - Re: [Intel-gfx] [PATCH 6/7] drm/i915: Try harder during dp pattern 1 link training

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Date:	Thu, 3 Nov 2011 13:03:29 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	Keith Packard <keithp@...thp.com>
Cc:	intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH 6/7] drm/i915: Try harder during dp pattern
 1 link training

On Tue,  1 Nov 2011 23:20:29 -0700
Keith Packard <keithp@...thp.com> wrote:

> Instead of going through the sequence just once, run through the whole
> set up to 5 times to see if something can work. This isn't part of the
> DP spec, but the BIOS seems to do it, and given that link training
> failure is so bad, it seems reasonable to follow suit.
> 
> Signed-off-by: Keith Packard <keithp@...thp.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c |   41 +++++++++++++++++++++++++-------------
>  1 files changed, 27 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 6be6a04..bf20a35 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -1576,8 +1576,9 @@ intel_dp_set_link_train(struct intel_dp *intel_dp,
>  
>  	ret = intel_dp_aux_native_write(intel_dp,
>  					DP_TRAINING_LANE0_SET,
> -					intel_dp->train_set, 4);
> -	if (ret != 4)
> +					intel_dp->train_set,
> +					intel_dp->lane_count);
> +	if (ret != intel_dp->lane_count)
>  		return false;
>  
>  	return true;

Sneaky putting this bug fix into this patch. :)

> @@ -1593,7 +1594,7 @@ intel_dp_start_link_train(struct intel_dp *intel_dp)
>  	int i;
>  	uint8_t voltage;
>  	bool clock_recovery = false;
> -	int tries;
> +	int voltage_tries, loop_tries;
>  	u32 reg;
>  	uint32_t DP = intel_dp->DP;
>  
> @@ -1620,7 +1621,8 @@ intel_dp_start_link_train(struct intel_dp *intel_dp)
>  		DP &= ~DP_LINK_TRAIN_MASK;
>  	memset(intel_dp->train_set, 0, 4);
>  	voltage = 0xff;
> -	tries = 0;
> +	voltage_tries = 0;
> +	loop_tries = 0;
>  	clock_recovery = false;
>  	for (;;) {
>  		/* Use intel_dp->train_set[0] to set the voltage and pre emphasis values */
> @@ -1663,17 +1665,28 @@ intel_dp_start_link_train(struct intel_dp *intel_dp)
>  		for (i = 0; i < intel_dp->lane_count; i++)
>  			if ((intel_dp->train_set[i] & DP_TRAIN_MAX_SWING_REACHED) == 0)
>  				break;
> -		if (i == intel_dp->lane_count)
> -			break;
> -
> -		/* Check to see if we've tried the same voltage 5 times */
> -		if ((intel_dp->train_set[0] & DP_TRAIN_VOLTAGE_SWING_MASK) == voltage) {
> -			++tries;
> -			if (tries == 5)
> +		if (i == intel_dp->lane_count) {
> +			++loop_tries;
> +			if (loop_tries == 5) {
> +				DRM_DEBUG_KMS("too many full retries, give up\n");
>  				break;
> -		} else
> -			tries = 0;
> -		voltage = intel_dp->train_set[0] & DP_TRAIN_VOLTAGE_SWING_MASK;
> +			}
> +			memset(intel_dp->train_set, 0, 4);
> +			voltage_tries = 0;
> +			continue;
> +		} else {
> +
> +			/* Check to see if we've tried the same voltage 5 times */
> +			if ((intel_dp->train_set[0] & DP_TRAIN_VOLTAGE_SWING_MASK) == voltage) {
> +				++voltage_tries;
> +				if (voltage_tries == 5) {
> +					DRM_DEBUG_KMS("too many voltage retries, give up\n");
> +					break;
> +				}
> +			} else
> +				voltage_tries = 0;
> +			voltage = intel_dp->train_set[0] & DP_TRAIN_VOLTAGE_SWING_MASK;
> +		}
>  
>  		/* Compute new intel_dp->train_set as requested by target */
>  		intel_get_adjust_train(intel_dp, link_status);

Don't you love the training state machine?  I think this looks ok, and
the DP compliance test should catch any grievous errors, so aside from
the bug fix hunk which should be split out:

Reviewed-by: Jesse Barnes <jbarnes@...tuousgeek.org>

-- 
Jesse Barnes, Intel Open Source Technology Center

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