drm/i915: Read HDCP R0 thrice in case of mismatch

As per DP spec when R0 mismatch is detected, HDCP source supported
re-read the R0 atleast twice.

And For HDMI and DP minimum wait required for the R0 availability is
100mSec. So this patch changes the wait time to 100mSec but retries
twice with the time interval of 100mSec for each attempt.

This patch is needed for DP HDCP1.4 CTS Test: 1A-06.

v2:
  No Change
v3:
  Comment on R0 retry is moved closer to the code[Seanpaul]
v4:
  Removing unwanted noise introduced in v3.

Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1522669822-2508-1-git-send-email-ramalingam.c@intel.com

drivers/gpu/drm/i915/intel_hdcp.c

@@ -506,15 +506,26 @@ static int intel_hdcp_auth(struct intel_digital_port *intel_dig_port,
 	 */
 	wait_remaining_ms_from_jiffies(r0_prime_gen_start, 300);
 
-	ri.reg = 0;
-	ret = shim->read_ri_prime(intel_dig_port, ri.shim);
-	if (ret)
-		return ret;
-	I915_WRITE(PORT_HDCP_RPRIME(port), ri.reg);
+	tries = 3;
 
-	/* Wait for Ri prime match */
-	if (wait_for(I915_READ(PORT_HDCP_STATUS(port)) &
-		     (HDCP_STATUS_RI_MATCH | HDCP_STATUS_ENC), 1)) {
+	/*
+	 * DP HDCP Spec mandates the two more reattempt to read R0, incase
+	 * of R0 mismatch.
+	 */
+	for (i = 0; i < tries; i++) {
+		ri.reg = 0;
+		ret = shim->read_ri_prime(intel_dig_port, ri.shim);
+		if (ret)
+			return ret;
+		I915_WRITE(PORT_HDCP_RPRIME(port), ri.reg);
+
+		/* Wait for Ri prime match */
+		if (!wait_for(I915_READ(PORT_HDCP_STATUS(port)) &
+		    (HDCP_STATUS_RI_MATCH | HDCP_STATUS_ENC), 1))
+			break;
+	}
+
+	if (i == tries) {
 		DRM_ERROR("Timed out waiting for Ri prime match (%x)\n",
 			  I915_READ(PORT_HDCP_STATUS(port)));
 		return -ETIMEDOUT;