can: c_can: Speed up tx buffer invalidation

It's suffcient to kill the TXIE bit in the message control register
even if the documentation of C and D CAN says that it's not allowed to
do that while MSGVAL is set. Reality tells a different story and this
change gives us another 2% of CPU back for not waiting on I/O.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Alexander Stein <alexander.stein@systec-electronic.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

2 files changed, 40 insertions, 15 deletions

diff --git a/drivers/net/can/c_can/c_can.c b/drivers/net/can/c_can/c_can.c
index 99d36bf1ba21..a2ca820b5373 100644
--- a/drivers/net/can/c_can/c_can.c
+++ b/drivers/net/can/c_can/c_can.c
@@ -276,11 +276,34 @@ static inline void c_can_object_put(struct net_device *dev, int iface,
         c_can_obj_update(dev, iface, cmd | IF_COMM_WR, obj);
 }
 
+/*
+ * Note: According to documentation clearing TXIE while MSGVAL is set
+ * is not allowed, but works nicely on C/DCAN. And that lowers the I/O
+ * load significantly.
+ */
+static void c_can_inval_tx_object(struct net_device *dev, int iface, int obj)
+{
+        struct c_can_priv *priv = netdev_priv(dev);
+
+        priv->write_reg(priv, C_CAN_IFACE(MSGCTRL_REG, iface), 0);
+        c_can_object_put(dev, iface, obj, IF_COMM_INVAL);
+}
+
+static void c_can_inval_msg_object(struct net_device *dev, int iface, int obj)
+{
+        struct c_can_priv *priv = netdev_priv(dev);
+
+        priv->write_reg(priv, C_CAN_IFACE(ARB1_REG, iface), 0);
+        priv->write_reg(priv, C_CAN_IFACE(ARB2_REG, iface), 0);
+        c_can_inval_tx_object(dev, iface, obj);
+}
+
 static void c_can_setup_tx_object(struct net_device *dev, int iface,
-                                  struct can_frame *frame, int obj)
+                                  struct can_frame *frame, int idx)
 {
         struct c_can_priv *priv = netdev_priv(dev);
         u16 ctrl = IF_MCONT_TX | frame->can_dlc;
+        bool rtr = frame->can_id & CAN_RTR_FLAG;
         u32 arb = IF_ARB_MSGVAL;
         int i;
 
@@ -291,9 +314,20 @@ static void c_can_setup_tx_object(struct net_device *dev, int iface,
                 arb |= (frame->can_id & CAN_SFF_MASK) << 18;
         }
 
-        if (!(frame->can_id & CAN_RTR_FLAG))
+        if (!rtr)
                 arb |= IF_ARB_TRANSMIT;
 
+        /*
+         * If we change the DIR bit, we need to invalidate the buffer
+         * first, i.e. clear the MSGVAL flag in the arbiter.
+         */
+        if (rtr != (bool)test_bit(idx, &priv->tx_dir)) {
+                u32 obj = idx + C_CAN_MSG_OBJ_TX_FIRST;
+
+                c_can_inval_msg_object(dev, iface, obj);
+                change_bit(idx, &priv->tx_dir);
+        }
+
         priv->write_reg(priv, C_CAN_IFACE(ARB1_REG, iface), arb);
         priv->write_reg(priv, C_CAN_IFACE(ARB2_REG, iface), arb >> 16);
 
@@ -401,17 +435,6 @@ static void c_can_setup_receive_object(struct net_device *dev, int iface,
         c_can_object_put(dev, iface, obj, IF_COMM_RCV_SETUP);
 }
 
-static void c_can_inval_msg_object(struct net_device *dev, int iface, int obj)
-{
-        struct c_can_priv *priv = netdev_priv(dev);
-
-        priv->write_reg(priv, C_CAN_IFACE(ARB1_REG, iface), 0);
-        priv->write_reg(priv, C_CAN_IFACE(ARB2_REG, iface), 0);
-        priv->write_reg(priv, C_CAN_IFACE(MSGCTRL_REG, iface), 0);
-
-        c_can_object_put(dev, iface, obj, IF_COMM_INVAL);
-}
-
 static netdev_tx_t c_can_start_xmit(struct sk_buff *skb,
                                     struct net_device *dev)
 {
@@ -436,7 +459,7 @@ static netdev_tx_t c_can_start_xmit(struct sk_buff *skb,
          * can_put_echo_skb(). We must do this before we enable
          * transmit as we might race against do_tx().
          */
-        c_can_setup_tx_object(dev, IF_TX, frame, obj);
+        c_can_setup_tx_object(dev, IF_TX, frame, idx);
         priv->dlc[idx] = frame->can_dlc;
         can_put_echo_skb(skb, dev, idx);
 
@@ -563,6 +586,7 @@ static int c_can_chip_config(struct net_device *dev)
         /* Clear all internal status */
         atomic_set(&priv->tx_active, 0);
         priv->rxmasked = 0;
+        priv->tx_dir = 0;
 
         /* set bittiming params */
         return c_can_set_bittiming(dev);
@@ -654,7 +678,7 @@ static void c_can_do_tx(struct net_device *dev)
                 idx--;
                 pend &= ~(1 << idx);
                 obj = idx + C_CAN_MSG_OBJ_TX_FIRST;
-                c_can_inval_msg_object(dev, IF_RX, obj);
+                c_can_inval_tx_object(dev, IF_RX, obj);
                 can_get_echo_skb(dev, idx);
                 bytes += priv->dlc[idx];
                 pkts++;
diff --git a/drivers/net/can/c_can/c_can.h b/drivers/net/can/c_can/c_can.h
index a5f10a01e49f..e7de2b9f26bb 100644
--- a/drivers/net/can/c_can/c_can.h
+++ b/drivers/net/can/c_can/c_can.h
@@ -174,6 +174,7 @@ struct c_can_priv {
         struct net_device *dev;
         struct device *device;
         atomic_t tx_active;
+        unsigned long tx_dir;
         int last_status;
         u16 (*read_reg) (struct c_can_priv *priv, enum reg index);
         void (*write_reg) (struct c_can_priv *priv, enum reg index, u16 val);