media: tegra-cec: reset rx_buf_cnt when start bit detected

If a start bit is detected, then reset the receive buffer counter to 0.

This ensures that no stale data is in the buffer if a message is
broken off midstream due to e.g. a Low Drive condition and then
retransmitted.

The only Rx interrupts we need to listen to are RX_REGISTER_FULL (i.e.
a valid byte was received) and RX_START_BIT_DETECTED (i.e. a new
message starts and we need to reset the counter).

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Cc: <stable@vger.kernel.org>      # for v4.15 and up
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/platform/tegra-cec/tegra_cec.c

@@ -172,16 +172,13 @@ static irqreturn_t tegra_cec_irq_handler(int irq, void *data)
 		}
 	}
 
-	if (status & (TEGRA_CEC_INT_STAT_RX_REGISTER_OVERRUN |
-		      TEGRA_CEC_INT_STAT_RX_BUS_ANOMALY_DETECTED |
-		      TEGRA_CEC_INT_STAT_RX_START_BIT_DETECTED |
-		      TEGRA_CEC_INT_STAT_RX_BUS_ERROR_DETECTED)) {
+	if (status & TEGRA_CEC_INT_STAT_RX_START_BIT_DETECTED) {
 		cec_write(cec, TEGRA_CEC_INT_STAT,
-			  (TEGRA_CEC_INT_STAT_RX_REGISTER_OVERRUN |
-			   TEGRA_CEC_INT_STAT_RX_BUS_ANOMALY_DETECTED |
-			   TEGRA_CEC_INT_STAT_RX_START_BIT_DETECTED |
-			   TEGRA_CEC_INT_STAT_RX_BUS_ERROR_DETECTED));
-	} else if (status & TEGRA_CEC_INT_STAT_RX_REGISTER_FULL) {
+			  TEGRA_CEC_INT_STAT_RX_START_BIT_DETECTED);
+		cec->rx_done = false;
+		cec->rx_buf_cnt = 0;
+	}
+	if (status & TEGRA_CEC_INT_STAT_RX_REGISTER_FULL) {
 		u32 v;
 
 		cec_write(cec, TEGRA_CEC_INT_STAT,
@@ -255,7 +252,7 @@ static int tegra_cec_adap_enable(struct cec_adapter *adap, bool enable)
 		  TEGRA_CEC_INT_MASK_TX_BUS_ANOMALY_DETECTED |
 		  TEGRA_CEC_INT_MASK_TX_FRAME_TRANSMITTED |
 		  TEGRA_CEC_INT_MASK_RX_REGISTER_FULL |
-		  TEGRA_CEC_INT_MASK_RX_REGISTER_OVERRUN);
+		  TEGRA_CEC_INT_MASK_RX_START_BIT_DETECTED);
 
 	cec_write(cec, TEGRA_CEC_HW_CONTROL, TEGRA_CEC_HWCTRL_TX_RX_MODE);
 	return 0;