[PATCH 3.19.y-ckt 095/128] can: sja1000: clear interrupts on start

[Kamal Mostafa]

3.19.8-ckt12 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mirza Krak <mirza.krak at hostmobility.com>

commit 7cecd9ab80f43972c056dc068338f7bcc407b71c upstream.

According to SJA1000 data sheet error-warning (EI) interrupt is not
cleared by setting the controller in to reset-mode.

Then if we have the following case:
- system is suspended (echo mem > /sys/power/state) and SJA1000 is left
  in operating state
- A bus error condition occurs which activates EI interrupt, system is
  still suspended which means EI interrupt will be not be handled nor
  cleared.

If the above two events occur, on resume there is no way to return the
SJA1000 to operating state, except to cycle power to it.

By simply reading the IR register on start we will clear any previous
conditions that could be present.

Signed-off-by: Mirza Krak <mirza.krak at hostmobility.com>
Reported-by: Christian Magnusson <Christian.Magnusson at semcon.com>
Signed-off-by: Marc Kleine-Budde <mkl at pengutronix.de>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/net/can/sja1000/sja1000.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/can/sja1000/sja1000.c b/drivers/net/can/sja1000/sja1000.c
index 32bd7f4..0c048e2 100644
--- a/drivers/net/can/sja1000/sja1000.c
+++ b/drivers/net/can/sja1000/sja1000.c
@@ -218,6 +218,9 @@ static void sja1000_start(struct net_device *dev)
 	priv->write_reg(priv, SJA1000_RXERR, 0x0);
 	priv->read_reg(priv, SJA1000_ECC);
 
+	/* clear interrupt flags */
+	priv->read_reg(priv, SJA1000_IR);
+
 	/* leave reset mode */
 	set_normal_mode(dev);
 }
-- 
1.9.1