can: mcp251x: write intf only when needed

This patch introduces a variable "clear_intf" that hold the bits that
should be cleared. Only read-modify-write register if "clear_intf"
is set.

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 7e2f951..f5e2edd 100644 (file)
--- a/drivers/net/can/mcp251x.c
+++ b/drivers/net/can/mcp251x.c
@@ -125,6 +125,8 @@
 #  define CANINTF_TX0IF 0x04
 #  define CANINTF_RX1IF 0x02
 #  define CANINTF_RX0IF 0x01
+#  define CANINTF_ERR_TX \
+       (CANINTF_ERRIF | CANINTF_TX2IF | CANINTF_TX1IF | CANINTF_TX0IF)
 #define EFLG         0x2d
 #  define EFLG_EWARN   0x01
 #  define EFLG_RXWAR   0x02
@@ -769,10 +771,12 @@ static irqreturn_t mcp251x_can_ist(int irq, void *dev_id)
        while (!priv->force_quit) {
                enum can_state new_state;
                u8 intf, eflag;
+               u8 clear_intf = 0;
                int can_id = 0, data1 = 0;
 
                mcp251x_read_2regs(spi, CANINTF, &intf, &eflag);
 
+               /* receive buffer 0 */
                if (intf & CANINTF_RX0IF) {
                        mcp251x_hw_rx(spi, 0);
                        /* Free one buffer ASAP */
@@ -780,10 +784,17 @@ static irqreturn_t mcp251x_can_ist(int irq, void *dev_id)
                                           0x00);
                }
 
-               if (intf & CANINTF_RX1IF)
+               /* receive buffer 1 */
+               if (intf & CANINTF_RX1IF) {
                        mcp251x_hw_rx(spi, 1);
+                       clear_intf |= CANINTF_RX1IF;
+               }
 
-               mcp251x_write_bits(spi, CANINTF, intf, 0x00);
+               /* any error or tx interrupt we need to clear? */
+               if (intf & CANINTF_ERR_TX)
+                       clear_intf |= intf & CANINTF_ERR_TX;
+               if (clear_intf)
+                       mcp251x_write_bits(spi, CANINTF, clear_intf, 0x00);
 
                if (eflag)
                        mcp251x_write_bits(spi, EFLG, eflag, 0x00);