[PATCH] can: at91_can: fix passive-state AERR flooding

[Brandon Maier]

When the at91_can is a single node on the bus and a user attempts to
transmit, the can state machine will report ack errors and increment the
transmit error count until it reaches the passive-state. Per the
specification, it will then transmit with a passive error, but will stop
incrementing the transmit error count. This results in the host machine
being flooded with the AERR interrupt forever, or until another node
rejoins the bus.

To prevent the AERR flooding, disable the AERR interrupt when we are in
passive mode.

Signed-off-by: Brandon Maier <brandon.maier@xxxxxxxxxxxxxxxxxxx>
---
 drivers/net/can/at91_can.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/net/can/at91_can.c b/drivers/net/can/at91_can.c
index b06af90a9964..2a8831127bd0 100644
--- a/drivers/net/can/at91_can.c
+++ b/drivers/net/can/at91_can.c
@@ -804,8 +804,13 @@ static int at91_poll(struct napi_struct *napi, int quota)
 		work_done += at91_poll_err(dev, quota - work_done, reg_sr);
 
 	if (work_done < quota) {
-		/* enable IRQs for frame errors and all mailboxes >= rx_next */
+		/* enable IRQs for frame errors and all mailboxes >= rx_next,
+		 * disable the ack error in passive mode to avoid flooding
+		 * ourselves with interrupts
+		 */
 		u32 reg_ier = AT91_IRQ_ERR_FRAME;
+		if (priv->can.state == CAN_STATE_ERROR_PASSIVE)
+			reg_ier &= ~AT91_IRQ_AERR;
 
 		reg_ier |= get_irq_mb_rx(priv) & ~AT91_MB_MASK(priv->rx_next);
 
-- 
2.30.2