[PATCH 3.19-rc3] c_can: SIE disabled when berr-reporting is off to reduce irq flood

[Viktor Babrian <babrian.viktor@renyi.mta.hu>]

Status interrupt is to be disabled if bus error reporting is off in order 
to reduce interrupt flood when e.g. a frame is not acked. Side effect is 
that when berr-reporting off, warn->pass and pass-warn state transitions 
may be reported later (upon a successful rx/tx event) or even go 
undetected. With proper implementation, these transitions could always be 
detected (but still later). It is considered better to have a non-accurate 
report of these transitions than having a non-responding system in 
possible scenarios.

Signed-off-by: Viktor Babrian <babrian.viktor@renyi.mta.hu>
---
--- linux-3.19-rc3/drivers/net/can/c_can/c_can.c	2015-01-06 
02:05:20.000000000 +0100
+++ linux/drivers/net/can/c_can/c_can.c	2015-01-18 17:46:09.000000000 
+0100
@@ -242,8 +242,11 @@ static void c_can_irq_control(struct c_c
  {
  	u32 ctrl = priv->read_reg(priv,	C_CAN_CTRL_REG) & ~CONTROL_IRQMSK;

+	/* do not enable status irq if bus error reporting is not needed 
*/
  	if (enable)
-		ctrl |= CONTROL_IRQMSK;
+		ctrl |= (priv->can.ctrlmode & CAN_CTRLMODE_BERR_REPORTING) 
?
+			CONTROL_IRQMSK :
+			(CONTROL_IRQMSK & ~CONTROL_SIE);

  	priv->write_reg(priv, C_CAN_CTRL_REG, ctrl);
  }