[PATCH] can: m_can: m_can_rx_handler(): fix RX in periphs being blocked by error handling

* [PATCH] can: m_can: m_can_rx_handler(): fix RX in periphs being blocked by error handling
@ 2021-03-03 12:49 Torin Cooper-Bennun
  2021-03-03 12:55 ` Marc Kleine-Budde
  0 siblings, 1 reply; 6+ messages in thread
From: Torin Cooper-Bennun @ 2021-03-03 12:49 UTC (permalink / raw)
  To: linux-can; +Cc: mkl, Torin Cooper-Bennun

In peripherals, m_can_rx_handler is called with quota = 1 from an ISR
context. If the M_CAN reports a high volume of errors, such as message
loss due to heavy bus traffic, then error handling, which is prioritised
in m_can_rx_handler, fills the quota immediately, and RX does not occur.
This has been observed to cause an indefinite blocking of RX.

The patch fixes this by ensuring that in peripherals, m_can_do_rx_poll
is always called with a quota of at least 1, regardless of any errors
handled.

This has been tested with the TCAN4550 under heavy bus traffic; message
loss is still detected correctly.

Signed-off-by: Torin Cooper-Bennun <torin@maxiluxsystems.com>
---
 drivers/net/can/m_can/m_can.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c
index 3752520a7d4b..3ec42e613ca1 100644
--- a/drivers/net/can/m_can/m_can.c
+++ b/drivers/net/can/m_can/m_can.c
@@ -866,8 +866,14 @@ static int m_can_rx_handler(struct net_device *dev, int quota)
 	if (irqstatus & IR_ERR_BUS_30X)
 		work_done += m_can_handle_bus_errors(dev, irqstatus, psr);
 
-	if (irqstatus & IR_RF0N)
-		work_done += m_can_do_rx_poll(dev, (quota - work_done));
+	if (irqstatus & IR_RF0N) {
+		int rx_quota = quota - work_done;
+
+		if (cdev->is_peripheral && (rx_quota <= 0))
+			rx_quota = 1;
+
+		work_done += m_can_do_rx_poll(dev, rx_quota);
+	}
 end:
 	return work_done;
 }
-- 
2.30.1


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