[Intel-gfx] [PATCH] drm/i915/dp: wait for previous AUX channel activity to clear

[Jesse Barnes]

Before initiating a new read or write on the DP AUX channel, wait for
any outstanding activity to complete.  This may happen during normal
retry behavior.  If the wait fails (i.e. after 1ms the AUX channel is
still busy) dump a backtrace to make the caller easier to spot.

Fixes https://bugs.freedesktop.org/show_bug.cgi?id=38136.

Signed-off-by: Jesse Barnes <jbarnes at virtuousgeek.org>
---
 drivers/gpu/drm/i915/intel_dp.c |   14 +++++++++++---
 1 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 4493641..34fbe7b 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -315,9 +315,17 @@ intel_dp_aux_ch(struct intel_dp *intel_dp,
 	else
 		precharge = 5;
 
-	if (I915_READ(ch_ctl) & DP_AUX_CH_CTL_SEND_BUSY) {
-		DRM_ERROR("dp_aux_ch not started status 0x%08x\n",
-			  I915_READ(ch_ctl));
+	/* Try to wait for any previous AUX channel activity */
+	for (try = 0; try < 10; try++) {
+		status = I915_READ(ch_ctl);
+		if ((status & DP_AUX_CH_CTL_SEND_BUSY) == 0)
+			break;
+		udelay(100);
+	}
+
+	if (try == 10) {
+		WARN(1, "dp_aux_ch not started status 0x%08x\n",
+		     I915_READ(ch_ctl));
 		return -EBUSY;
 	}
 
-- 
1.7.4.1