[Intel-gfx] [PATCHv3] drm/i915/dp: Change aux_ctl reg read to polling read

[Arun R Murthy <arun.r.murthy@intel.com>]

The busy timeout logic checks for the AUX BUSY, then waits for the
timeout period and then after timeout reads the register for BUSY or
Success.
Instead replace interrupt with polling so as to read the AUX CTL
register often before the timeout period. Looks like there might be some
issue with interrupt-on-read. Hence changing the logic to polling read.

v2: replace interrupt with polling read
v3: use usleep_rang instead of msleep, updated commit msg

Signed-off-by: Arun R Murthy <arun.r.murthy@intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp_aux.c | 24 ++++++++++++---------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux.c b/drivers/gpu/drm/i915/display/intel_dp_aux.c
index 664bebdecea7..878452e6e37f 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_aux.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c
@@ -40,21 +40,25 @@ intel_dp_aux_wait_done(struct intel_dp *intel_dp)
 	i915_reg_t ch_ctl = intel_dp->aux_ch_ctl_reg(intel_dp);
 	const unsigned int timeout_ms = 10;
 	u32 status;
-	bool done;
+	int try;
 
-#define C (((status = intel_uncore_read_notrace(&i915->uncore, ch_ctl)) & DP_AUX_CH_CTL_SEND_BUSY) == 0)
-	done = wait_event_timeout(i915->display.gmbus.wait_queue, C,
-				  msecs_to_jiffies_timeout(timeout_ms));
+	for (try = 0; try < 10; try++) {
+		status = intel_uncore_read_notrace(&i915->uncore, ch_ctl);
+		if ((status & DP_AUX_CH_CTL_SEND_BUSY) == 0)
+			break;
+		usleep_range(400, 500);
+	}
 
+	if (try == 3) {
+		status = intel_uncore_read_notrace(&i915->uncore, ch_ctl);
+		if ((status & DP_AUX_CH_CTL_SEND_BUSY) != 0)
+			drm_err(&i915->drm,
+				"%s: did not complete or timeout within %ums (status 0x%08x)\n",
+				intel_dp->aux.name, timeout_ms, status);
+	}
 	/* just trace the final value */
 	trace_i915_reg_rw(false, ch_ctl, status, sizeof(status), true);
 
-	if (!done)
-		drm_err(&i915->drm,
-			"%s: did not complete or timeout within %ums (status 0x%08x)\n",
-			intel_dp->aux.name, timeout_ms, status);
-#undef C
-
 	return status;
 }
 
-- 
2.25.1