can: mcp251x: read-modify-write eflag only when needed

Use read-modify-write instead of a simple write to change the register
contents, to close existing the race window between the original manual
read and write.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Acked-by: Wolfgang Grandegger <wg@grandegger.com>

diff --git a/drivers/net/can/mcp251x.c b/drivers/net/can/mcp251x.c
index 9b3466a..7e2f951 100644 (file)
--- a/drivers/net/can/mcp251x.c
+++ b/drivers/net/can/mcp251x.c
@@ -785,7 +785,8 @@ static irqreturn_t mcp251x_can_ist(int irq, void *dev_id)
 
                mcp251x_write_bits(spi, CANINTF, intf, 0x00);
 
-               mcp251x_write_reg(spi, EFLG, 0x00);
+               if (eflag)
+                       mcp251x_write_bits(spi, EFLG, eflag, 0x00);
 
                /* Update can state */
                if (eflag & EFLG_TXBO) {