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

From: Jesse Barnes <jbarnes@virtuousgeek.org>
To: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Cc: intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH] drm/i915: make DP training try a little harder
Date: Wed, 5 Jan 2011 09:19:19 -0800	[thread overview]
Message-ID: <20110105091919.6da339d9@jbarnes-desktop> (raw)
In-Reply-To: <20110105075239.GA2702@yliu-dev.sh.intel.com>

On Wed, 5 Jan 2011 15:52:39 +0800
Yuanhan Liu <yuanhan.liu@linux.intel.com> wrote:

> 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.

Does this one at least keep it from hanging?

If it doesn't actually help with suspend/resume, I wonder if we need to
use fast link training on that machine.  The "use VBT provided values"
patch did that, using the VBT pre-emphasis and vswing values, but we
can also cache the last known good AUX handshake data and use that at
resume time too.  Can you give that a try?

Thanks,
-- 
Jesse Barnes, Intel Open Source Technology Center

>From fdb4552b4da707bfa5f3ab9e5dd92f04b39e41d3 Mon Sep 17 00:00:00 2001
From: Jesse Barnes <jbarnes@virtuousgeek.org>
Date: Tue, 4 Jan 2011 11:50:32 -0800
Subject: [PATCH] drm/i915: make DP training try a little harder

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 |   27 +++++++++++++++++++++++----
 1 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 1dc6040..c768e30 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1334,17 +1334,24 @@ 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 */
 		uint32_t    signal_levels;
 
+		if (cr_tries > 5) {
+			DRM_ERROR("failed to train DP, aborting\n");
+			intel_dp_link_down(intel_dp);
+			break;
+		}
+
 		if (IS_GEN6(dev) && is_edp(intel_dp)) {
 			signal_levels = intel_gen6_edp_signal_levels(intel_dp->train_set[0]);
 			DP = (DP & ~EDP_LINK_TRAIN_VOL_EMP_MASK_SNB) | signal_levels;
@@ -1367,14 +1374,26 @@ 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;
+		}
+
 		if (intel_channel_eq_ok(intel_dp)) {
 			channel_eq = true;
 			break;
 		}
 
-		/* Try 5 times */
-		if (tries > 5)
-			break;
+		/* 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++;
+			continue;
+		}
 
 		/* Compute new intel_dp->train_set as requested by target */
 		intel_get_adjust_train(intel_dp);
-- 
1.7.0.4
