[PATCH 1/3] net can c_can: only read status register after status irq

[Kurt Van Dijck <dev.kurt@xxxxxxxxxxxxxxxxxxxxxx>]

When the status register is read without status irq pending,
it may get into a state that it goes into busoff state
without having its irq activated, so the driver wil never know.
Thanks to Wolfgang and Joe for bringing up the first idea.

Signed-off-by: Kurt Van Dijck <dev.kurt@xxxxxxxxxxxxxxxxxxxxxx>
CC: Wolfgang Grandegger <wg@xxxxxxxxxxxxxx>
CC: Joe Burmeister <joe.burmeister@xxxxxxxxxxxxx>
---
 drivers/net/can/c_can/c_can.c | 24 +++++++++++++++++++-----
 drivers/net/can/c_can/c_can.h |  1 +
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/drivers/net/can/c_can/c_can.c b/drivers/net/can/c_can/c_can.c
index 606b7d8..b8e395a3 100644
--- a/drivers/net/can/c_can/c_can.c
+++ b/drivers/net/can/c_can/c_can.c
@@ -97,6 +97,9 @@
 #define BTR_TSEG2_SHIFT		12
 #define BTR_TSEG2_MASK		(0x7 << BTR_TSEG2_SHIFT)
 
+/* interrupt register */
+#define INT_STS_PENDING		0x8000
+
 /* brp extension register */
 #define BRP_EXT_BRPE_MASK	0x0f
 #define BRP_EXT_BRPE_SHIFT	0
@@ -1029,10 +1032,15 @@ static int c_can_poll(struct napi_struct *napi, int quota)
 	u16 curr, last = priv->last_status;
 	int work_done = 0;
 
-	priv->last_status = curr = priv->read_reg(priv, C_CAN_STS_REG);
-	/* Ack status on C_CAN. D_CAN is self clearing */
-	if (priv->type != BOSCH_D_CAN)
-		priv->write_reg(priv, C_CAN_STS_REG, LEC_UNUSED);
+	/* Only read the status register if a status interrupt was pending */
+	if (atomic_xchg(&priv->sie_pending, 0)) {
+		priv->last_status = curr = priv->read_reg(priv, C_CAN_STS_REG);
+		/* Ack status on C_CAN. D_CAN is self clearing */
+		if (priv->type != BOSCH_D_CAN)
+			priv->write_reg(priv, C_CAN_STS_REG, LEC_UNUSED);
+	} else
+		/* no change detected ... */
+		curr = last;
 
 	/* handle state changes */
 	if ((curr & STATUS_EWARN) && (!(last & STATUS_EWARN))) {
@@ -1083,10 +1091,16 @@ static irqreturn_t c_can_isr(int irq, void *dev_id)
 {
 	struct net_device *dev = (struct net_device *)dev_id;
 	struct c_can_priv *priv = netdev_priv(dev);
+	int intreg;
 
-	if (!priv->read_reg(priv, C_CAN_INT_REG))
+	intreg = priv->read_reg(priv, C_CAN_INT_REG);
+	if (!intreg)
 		return IRQ_NONE;
 
+	/* save for later use */
+	if (intreg & INT_STS_PENDING)
+		atomic_set(&priv->sie_pending, 1);
+
 	/* disable all interrupts and schedule the NAPI */
 	c_can_irq_control(priv, false);
 	napi_schedule(&priv->napi);
diff --git a/drivers/net/can/c_can/c_can.h b/drivers/net/can/c_can/c_can.h
index 8acdc7f..d5567a7 100644
--- a/drivers/net/can/c_can/c_can.h
+++ b/drivers/net/can/c_can/c_can.h
@@ -198,6 +198,7 @@ struct c_can_priv {
 	struct net_device *dev;
 	struct device *device;
 	atomic_t tx_active;
+	atomic_t sie_pending;
 	unsigned long tx_dir;
 	int last_status;
 	u16 (*read_reg) (const struct c_can_priv *priv, enum reg index);
-- 
1.8.5.rc3