drm/i915/dp: wait for previous AUX channel activity to clear

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. v2: use msleep instead, and timeout after 3ms (only ever saw 1 retry with msleep in testing) v3: fix backtrace check to trigger if the 3ms wait times out Fixes https://bugs.freedesktop.org/show_bug.cgi?id=38136. Signed-off-by: Jesse Barnes <[email protected]> Reviewed-by: Keith Packard <[email protected]> Signed-off-by: Keith Packard <[email protected]>
sasich · Aug 1, 2011 · 11bee43 · 11bee43
1 parent cda2bb7
commit 11bee43
Showing 1 changed file with 11 additions and 3 deletions.
diff --git 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 < 3; try++) {
+		status = I915_READ(ch_ctl);
+		if ((status & DP_AUX_CH_CTL_SEND_BUSY) == 0)
+			break;
+		msleep(1);
+	}
+
+	if (try == 3) {
+		WARN(1, "dp_aux_ch not started status 0x%08x\n",
+		     I915_READ(ch_ctl));
 		return -EBUSY;
 	}