[PATCHv2] media: cec: core: count low-drive, error and arb-lost conditions

[Hans Verkuil <hverkuil@xxxxxxxxx>]

Count how many Low Drive, Error and Arbitration Lost transmit
status errors occurred, and expose that in debugfs.

Also log the first 8 transmits that result in Low Drive or Error
conditions. That really should not happen with well-behaved CEC devices
and good HDMI cables.

This is useful to detect and debug HDMI cable issues.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
---
Changes since v1:
- Log the first 8 transmits that resulted in a Low Drive or Error status.
---
diff --git a/drivers/media/cec/core/cec-adap.c b/drivers/media/cec/core/cec-adap.c
index 09ca83c23329..f8f7ac61fe55 100644
--- a/drivers/media/cec/core/cec-adap.c
+++ b/drivers/media/cec/core/cec-adap.c
@@ -511,7 +511,7 @@ int cec_thread_func(void *_adap)
 				pr_warn("cec-%s: transmit timed out\n", adap->name);
 			}
 			adap->transmit_in_progress = false;
-			adap->tx_timeouts++;
+			adap->tx_timeout_cnt++;
 			goto unlock;
 		}

@@ -625,6 +625,33 @@ void cec_transmit_done_ts(struct cec_adapter *adap, u8 status,
 	msg->tx_low_drive_cnt += low_drive_cnt;
 	msg->tx_error_cnt += error_cnt;

+	adap->tx_arb_lost_cnt += arb_lost_cnt;
+	adap->tx_low_drive_cnt += low_drive_cnt;
+	adap->tx_error_cnt += error_cnt;
+
+	/*
+	 * Low Drive transmission errors should really not happen for
+	 * well-behaved CEC devices and proper HDMI cables.
+	 *
+	 * Ditto for the 'Error' status.
+	 *
+	 * For the first few times that this happens, log this.
+	 * Stop logging after that, since that will not add any more
+	 * useful information and instead it will just flood the kernel log.
+	 */
+	if (done && adap->tx_low_drive_log_cnt < 8 && msg->tx_low_drive_cnt) {
+		adap->tx_low_drive_log_cnt++;
+		dprintk(0, "low drive counter: %u (seq %u: %*ph)\n",
+		       	msg->tx_low_drive_cnt, msg->sequence,
+			msg->len, msg->msg);
+	}
+	if (done && adap->tx_error_log_cnt < 8 && msg->tx_error_cnt) {
+		adap->tx_error_log_cnt++;
+		dprintk(0, "error counter: %u (seq %u: %*ph)\n",
+		       	msg->tx_error_cnt, msg->sequence,
+			msg->len, msg->msg);
+	}
+
 	/* Mark that we're done with this transmit */
 	adap->transmitting = NULL;

@@ -1607,6 +1634,8 @@ int cec_adap_enable(struct cec_adapter *adap)
 	if (enable) {
 		adap->last_initiator = 0xff;
 		adap->transmit_in_progress = false;
+		adap->tx_low_drive_log_cnt = 0;
+		adap->tx_error_log_cnt = 0;
 		ret = adap->ops->adap_enable(adap, true);
 		if (!ret) {
 			/*
@@ -2260,10 +2289,25 @@ int cec_adap_status(struct seq_file *file, void *priv)
 	if (adap->monitor_pin_cnt)
 		seq_printf(file, "file handles in Monitor Pin mode: %u\n",
 			   adap->monitor_pin_cnt);
-	if (adap->tx_timeouts) {
-		seq_printf(file, "transmit timeouts: %u\n",
-			   adap->tx_timeouts);
-		adap->tx_timeouts = 0;
+	if (adap->tx_timeout_cnt) {
+		seq_printf(file, "transmit timeout count: %u\n",
+			   adap->tx_timeout_cnt);
+		adap->tx_timeout_cnt = 0;
+	}
+	if (adap->tx_low_drive_cnt) {
+		seq_printf(file, "transmit low drive count: %u\n",
+			   adap->tx_low_drive_cnt);
+		adap->tx_low_drive_cnt = 0;
+	}
+	if (adap->tx_arb_lost_cnt) {
+		seq_printf(file, "transmit arbitration lost count: %u\n",
+			   adap->tx_arb_lost_cnt);
+		adap->tx_arb_lost_cnt = 0;
+	}
+	if (adap->tx_error_cnt) {
+		seq_printf(file, "transmit error count: %u\n",
+			   adap->tx_error_cnt);
+		adap->tx_error_cnt = 0;
 	}
 	data = adap->transmitting;
 	if (data)
diff --git a/include/media/cec.h b/include/media/cec.h
index 53e4b2eb2b26..0b77ce9f2e65 100644
--- a/include/media/cec.h
+++ b/include/media/cec.h
@@ -262,7 +262,12 @@ struct cec_adapter {
 	struct cec_log_addrs log_addrs;
 	struct cec_connector_info conn_info;

-	u32 tx_timeouts;
+	u32 tx_timeout_cnt;
+	u32 tx_low_drive_cnt;
+	u32 tx_error_cnt;
+	u32 tx_arb_lost_cnt;
+	u32 tx_low_drive_log_cnt;
+	u32 tx_error_log_cnt;

 #ifdef CONFIG_CEC_NOTIFIER
 	struct cec_notifier *notifier;