[PATCH] drm/i915: Change order of operations for VLV/CHV to not train DP link before PHYs are ready

[Todd Previte <tprevite@gmail.com>]

Reorder the function calls in chv/vlv_pre_enable_dp() such that link training is not initiated
before the PHYs come up out of reset. Also check the status of vlv_wait_port_ready() and
only attempt to train if the PHYs are actually running.

The specification lists the wait for the PHYs as one of the final steps in enabling
the Displayport hardware for use.  While the PHYs are in reset, no communication is p
ossible across the link. Attempting to train the link while the PHYs are in reset will
result in link training failure with one or more WARN() in the logs. Moving the
intel_enable_dp() function after vlv_wait_port_ready() and only when the PHYs are ready
helps ensure reliable operation of the Displayport link.

Signed-off-by: Todd Previte <tprevite@gmail.com>
---
 drivers/gpu/drm/i915/intel_display.c |  8 ++++++--
 drivers/gpu/drm/i915/intel_dp.c      | 10 ++++------
 drivers/gpu/drm/i915/intel_drv.h     |  2 +-
 3 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index c51d950..4b280c1 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -1723,7 +1723,7 @@ static void chv_disable_pll(struct drm_i915_private *dev_priv, enum pipe pipe)
 	mutex_unlock(&dev_priv->dpio_lock);
 }
 
-void vlv_wait_port_ready(struct drm_i915_private *dev_priv,
+int vlv_wait_port_ready(struct drm_i915_private *dev_priv,
 		struct intel_digital_port *dport)
 {
 	u32 port_mask;
@@ -1746,9 +1746,13 @@ void vlv_wait_port_ready(struct drm_i915_private *dev_priv,
 		BUG();
 	}
 
-	if (wait_for((I915_READ(dpll_reg) & port_mask) == 0, 1000))
+	if (wait_for((I915_READ(dpll_reg) & port_mask) == 0, 1000)) {
 		WARN(1, "timed out waiting for port %c ready: 0x%08x\n",
 		     port_name(dport->port), I915_READ(dpll_reg));
+		return -EIO;
+	}
+
+	return 0;
 }
 
 static void intel_prepare_shared_dpll(struct intel_crtc *crtc)
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index a8352c4..ada8b07 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -2705,9 +2705,8 @@ static void vlv_pre_enable_dp(struct intel_encoder *encoder)
 		pps_unlock(intel_dp);
 	}
 
-	intel_enable_dp(encoder);
-
-	vlv_wait_port_ready(dev_priv, dport);
+	if (vlv_wait_port_ready(dev_priv, dport) == 0)
+	    intel_enable_dp(encoder);
 }
 
 static void vlv_dp_pre_pll_enable(struct intel_encoder *encoder)
@@ -2805,9 +2804,8 @@ static void chv_pre_enable_dp(struct intel_encoder *encoder)
 		pps_unlock(intel_dp);
 	}
 
-	intel_enable_dp(encoder);
-
-	vlv_wait_port_ready(dev_priv, dport);
+	if (vlv_wait_port_ready(dev_priv, dport) == 0)
+	    intel_enable_dp(encoder);
 }
 
 static void chv_dp_pre_pll_enable(struct intel_encoder *encoder)
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index dc80444..2ff2c8c 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -876,7 +876,7 @@ intel_wait_for_vblank(struct drm_device *dev, int pipe)
 	drm_wait_one_vblank(dev, pipe);
 }
 int ironlake_get_lanes_required(int target_clock, int link_bw, int bpp);
-void vlv_wait_port_ready(struct drm_i915_private *dev_priv,
+int vlv_wait_port_ready(struct drm_i915_private *dev_priv,
 			 struct intel_digital_port *dport);
 bool intel_get_load_detect_pipe(struct drm_connector *connector,
 				struct drm_display_mode *mode,
-- 
1.9.1