[Intel-gfx] [NOT_FOR_REVIEW PATCH] drm/i915/display/dp: On AUX xfer timeout restart freshly

[Arun R Murthy]

At the beginning of the aux transfer a check for aux control busy bit is
done. Then as per the spec on aux transfer timeout, need to retry
freshly for 3 times with a delay which is taken care by the control
register.
On each of these 3 trials a check for busy has to be done so as to start
freshly.

v2: updated the commit message
v4: check for SEND_BUSY after write (Imre)
v5: reverted the send_ctl to the while loop (Jani)

Signed-off-by: Arun R Murthy <arun.r.murthy at intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp_aux.c | 55 ++++++++++-----------
 1 file changed, 25 insertions(+), 30 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux.c b/drivers/gpu/drm/i915/display/intel_dp_aux.c
index 21b50a5c8a85..ca86b59b57f8 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_aux.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c
@@ -226,6 +226,7 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
 	int i, ret, recv_bytes;
 	int try, clock = 0;
 	u32 status;
+	u32 send_ctl;
 	bool vdd;
 
 	ch_ctl = intel_dp->aux_ch_ctl_reg(intel_dp);
@@ -273,30 +274,6 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
 	 * it using the same AUX CH simultaneously
 	 */
 
-	/* Try to wait for any previous AUX channel activity */
-	for (try = 0; try < 3; try++) {
-		status = intel_de_read_notrace(i915, ch_ctl);
-		if ((status & DP_AUX_CH_CTL_SEND_BUSY) == 0)
-			break;
-		msleep(1);
-	}
-	/* just trace the final value */
-	trace_i915_reg_rw(false, ch_ctl, status, sizeof(status), true);
-
-	if (try == 3) {
-		const u32 status = intel_de_read(i915, ch_ctl);
-
-		if (status != intel_dp->aux_busy_last_status) {
-			drm_WARN(&i915->drm, 1,
-				 "%s: not started (status 0x%08x)\n",
-				 intel_dp->aux.name, status);
-			intel_dp->aux_busy_last_status = status;
-		}
-
-		ret = -EBUSY;
-		goto out;
-	}
-
 	/* Only 5 data registers! */
 	if (drm_WARN_ON(&i915->drm, send_bytes > 20 || recv_size > 20)) {
 		ret = -E2BIG;
@@ -304,14 +281,31 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
 	}
 
 	while ((aux_clock_divider = intel_dp->get_aux_clock_divider(intel_dp, clock++))) {
-		u32 send_ctl = intel_dp->get_aux_send_ctl(intel_dp,
-							  send_bytes,
-							  aux_clock_divider);
+		/* FIXME: Must try at least 3 times according to DP spec */
+		for (try = 0; try < 5; try++) {
+			send_ctl = intel_dp->get_aux_send_ctl(intel_dp,
+							      send_bytes,
+							      aux_clock_divider);
+			send_ctl |= aux_send_ctl_flags;
 
-		send_ctl |= aux_send_ctl_flags;
+			/* Try to wait for any previous AUX channel activity */
+			status = intel_dp_aux_wait_done(intel_dp);
+			/* just trace the final value */
+			trace_i915_reg_rw(false, ch_ctl, status, sizeof(status), true);
+
+			if (status & DP_AUX_CH_CTL_SEND_BUSY) {
+				drm_WARN(&i915->drm, 1,
+					 "%s: not started, previous Tx still in process (status 0x%08x)\n",
+					 intel_dp->aux.name, status);
+				intel_dp->aux_busy_last_status = status;
+				if (try > 3) {
+					ret = -EBUSY;
+					goto out;
+				} else {
+					continue;
+				}
+			}
 
-		/* Must try at least 3 times according to DP spec */
-		for (try = 0; try < 5; try++) {
 			/* Load the send data into the aux channel data registers */
 			for (i = 0; i < send_bytes; i += 4)
 				intel_de_write(i915, ch_data[i >> 2],
@@ -321,6 +315,7 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
 			/* Send the command and wait for it to complete */
 			intel_de_write(i915, ch_ctl, send_ctl);
 
+			/* TODO: if typeC then 4.2ms else 800us. For DG2 add 1.5ms for both cases */
 			status = intel_dp_aux_wait_done(intel_dp);
 
 			/* Clear done status and any errors */
-- 
2.25.1