Re: [PATCH] drm/i915: make DP training try a little harder

[Yuanhan Liu <yuanhan.liu@linux.intel.com>]

On Tue, Jan 04, 2011 at 11:53:14AM -0800, Jesse Barnes wrote:
> When trying to do channel equalization, we need to make sure we still
> have clock recovery on all lanes while training.  We also need to try
> clock recovery again if we lose the clock or if channel eq fails 5
> times.  We'll try clock recovery up to 5 more times before giving up
> entirely.
> 
> Gets suspend/resume working on my Vaio again and brings us back into
> compliance with the DP training sequence spec.
> 
> Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
> ---
>  drivers/gpu/drm/i915/intel_dp.c |   25 ++++++++++++++++++++++---
>  1 files changed, 22 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 1dc6040..35152cb 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -1334,12 +1334,13 @@ intel_dp_complete_link_train(struct intel_dp *intel_dp)
>  	struct drm_device *dev = intel_dp->base.base.dev;
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  	bool channel_eq = false;
> -	int tries;
> +	int tries, cr_tries;
>  	u32 reg;
>  	uint32_t DP = intel_dp->DP;
>  
>  	/* channel equalization */
>  	tries = 0;
> +	cr_tries = 0;
>  	channel_eq = false;
>  	for (;;) {
>  		/* Use intel_dp->train_set[0] to set the voltage and pre emphasis values */
> @@ -1367,18 +1368,36 @@ intel_dp_complete_link_train(struct intel_dp *intel_dp)
>  		if (!intel_dp_get_link_status(intel_dp))
>  			break;
>  
> +		/* Make sure clock is still ok */
> +		if (!intel_clock_recovery_ok(intel_dp->link_status, intel_dp->lane_count)) {
> +			intel_dp_start_link_train(intel_dp);
> +			cr_tries++;
> +			continue;
> +		}
> +
Hi Jesse,

This will cause a endless loop when the clock recovery phase always
failed, just like what happend on my test machine.


And, FYI, the two patch would not fix bug
https://bugs.freedesktop.org/show_bug.cgi?id=32539
the train link still failed.


Thanks, 
Yuanhan Liu


>  		if (intel_channel_eq_ok(intel_dp)) {
>  			channel_eq = true;
>  			break;
>  		}
>  
> -		/* Try 5 times */
> -		if (tries > 5)
> +		/* Try 5 times, then try clock recovery if that fails */
> +		if (tries > 5) {
> +			intel_dp_link_down(intel_dp);
> +			intel_dp_start_link_train(intel_dp);
> +			tries = 0;
> +			cr_tries++;
>  			break;
> +		}
>  
>  		/* Compute new intel_dp->train_set as requested by target */
>  		intel_get_adjust_train(intel_dp);
>  		++tries;
> +
> +		if (cr_tries > 5) {
> +			DRM_ERROR("failed to train DP, aborting\n");
> +			intel_dp_link_down(intel_dp);
> +			break;
> +		}
>  	}
>  
>  	if (HAS_PCH_CPT(dev) && !is_edp(intel_dp))
> -- 
> 1.7.0.4
> 
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