[PATCH] drm/i915/hdcp: Retry first read and writes to downstream

[Suraj Kandpal]

Retry the first read and write to downstream at least 10 times
with a 50ms delay if not hdcp2 capable(dock decides to stop advertising
hdcp2 capability for some reason). The reason being that
during suspend resume Dock usually keep the HDCP2 registers inaccesible
causing AUX error. This wouldn't be a big problem if the userspace
just kept retrying with some delay while it continues to play low
values content but most userpace applications end up throwing an error
when it receives one from KMD. This makes sure we give the dock
and the sink devices to complete its power cycle and then try HDCP
authentication.

--v2
-Add more details in comment [Jani]
-fix looping condition [Jani]
-optimize loop exit condition [Jani]

--v3
-Add comment explaining why the loop was added [Ankit]

Signed-off-by: Suraj Kandpal <suraj.kandpal at intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
---
 drivers/gpu/drm/i915/display/intel_hdcp.c | 37 ++++++++++++++++++-----
 1 file changed, 30 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_hdcp.c b/drivers/gpu/drm/i915/display/intel_hdcp.c
index 2afa92321b08..00d4c9ac6c45 100644
--- a/drivers/gpu/drm/i915/display/intel_hdcp.c
+++ b/drivers/gpu/drm/i915/display/intel_hdcp.c
@@ -1512,7 +1512,7 @@ static int hdcp2_authentication_key_exchange(struct intel_connector *connector)
 	} msgs;
 	const struct intel_hdcp_shim *shim = hdcp->shim;
 	size_t size;
-	int ret;
+	int ret, i;
 
 	/* Init for seq_num */
 	hdcp->seq_num_v = 0;
@@ -1522,13 +1522,36 @@ static int hdcp2_authentication_key_exchange(struct intel_connector *connector)
 	if (ret < 0)
 		return ret;
 
-	ret = shim->write_2_2_msg(connector, &msgs.ake_init,
-				  sizeof(msgs.ake_init));
-	if (ret < 0)
-		return ret;
+	/*
+	 * Retry the first read and write to downstream at least 10 times
+	 * with a 50ms delay if not hdcp2 capable(dock decides to stop advertising
+	 * hdcp2 capability for some reason). The reason being that
+	 * during suspend resume dock usually keeps the HDCP2 registers inaccesible
+	 * causing AUX error. This wouldn't be a big problem if the userspace
+	 * just kept retrying with some delay while it continues to play low
+	 * value content but most userpace applications end up throwing an error
+	 * when it receives one from KMD. This makes sure we give the dock
+	 * and the sink devices to complete its power cycle and then try HDCP
+	 * authentication. The values of 10 and delay of 50ms was decided based
+	 * on multiple trial and errors.
+	 */
+	for (i = 0; i < 10; i++) {
+		if (!intel_hdcp2_get_capability(connector)) {
+			msleep(50);
+			continue;
+		}
+
+		ret = shim->write_2_2_msg(connector, &msgs.ake_init,
+					  sizeof(msgs.ake_init));
+		if (ret < 0)
+			continue;
+
+		ret = shim->read_2_2_msg(connector, HDCP_2_2_AKE_SEND_CERT,
+					 &msgs.send_cert, sizeof(msgs.send_cert));
+		if (ret > 0)
+			break;
+	}
 
-	ret = shim->read_2_2_msg(connector, HDCP_2_2_AKE_SEND_CERT,
-				 &msgs.send_cert, sizeof(msgs.send_cert));
 	if (ret < 0)
 		return ret;
 
-- 
2.43.2