can: c_can: support tx ring algorithm

The algorithm is already used successfully by other CAN drivers
(e.g. mcp251xfd). Its implementation was kindly suggested to me by
Marc Kleine-Budde following a patch I had previously submitted. You can
find every detail at https://lore.kernel.org/patchwork/patch/1422929/.

The idea is that after this patch, it will be easier to patch the driver
to use the message object memory as a true FIFO.

Link: https://lore.kernel.org/r/20210807130800.5246-4-dariobin@libero.it
Suggested-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Dario Binacchi <dariobin@libero.it>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

diff --git a/drivers/net/can/c_can/c_can.h b/drivers/net/can/c_can/c_can.h
index 8f23e9c..9b4e54c 100644 (file)
--- a/drivers/net/can/c_can/c_can.h
+++ b/drivers/net/can/c_can/c_can.h
@@ -176,6 +176,13 @@ struct c_can_raminit {
        bool needs_pulse;
 };
 
+/* c_can tx ring structure */
+struct c_can_tx_ring {
+       unsigned int head;
+       unsigned int tail;
+       unsigned int obj_num;
+};
+
 /* c_can private data structure */
 struct c_can_priv {
        struct can_priv can;    /* must be the first member */
@@ -190,10 +197,10 @@ struct c_can_priv {
        unsigned int msg_obj_tx_first;
        unsigned int msg_obj_tx_last;
        u32 msg_obj_rx_mask;
-       atomic_t tx_active;
        atomic_t sie_pending;
        unsigned long tx_dir;
        int last_status;
+       struct c_can_tx_ring tx;
        u16 (*read_reg)(const struct c_can_priv *priv, enum reg index);
        void (*write_reg)(const struct c_can_priv *priv, enum reg index, u16 val);
        u32 (*read_reg32)(const struct c_can_priv *priv, enum reg index);
@@ -219,4 +226,28 @@ int c_can_power_down(struct net_device *dev);
 
 void c_can_set_ethtool_ops(struct net_device *dev);
 
+static inline u8 c_can_get_tx_head(const struct c_can_tx_ring *ring)
+{
+       return ring->head & (ring->obj_num - 1);
+}
+
+static inline u8 c_can_get_tx_tail(const struct c_can_tx_ring *ring)
+{
+       return ring->tail & (ring->obj_num - 1);
+}
+
+static inline u8 c_can_get_tx_free(const struct c_can_tx_ring *ring)
+{
+       u8 head = c_can_get_tx_head(ring);
+       u8 tail = c_can_get_tx_tail(ring);
+
+       /* This is not a FIFO. C/D_CAN sends out the buffers
+        * prioritized. The lowest buffer number wins.
+        */
+       if (head < tail)
+               return 0;
+
+       return ring->obj_num - head;
+}
+
 #endif /* C_CAN_H */

diff --git a/drivers/net/can/c_can/c_can_main.c b/drivers/net/can/c_can/c_can_main.c
index 1ec0ce6..eb324ff 100644 (file)
--- a/drivers/net/can/c_can/c_can_main.c
+++ b/drivers/net/can/c_can/c_can_main.c
@@ -427,24 +427,50 @@ 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 bool c_can_tx_busy(const struct c_can_priv *priv,
+                         const struct c_can_tx_ring *tx_ring)
+{
+       if (c_can_get_tx_free(tx_ring) > 0)
+               return false;
+
+       netif_stop_queue(priv->dev);
+
+       /* Memory barrier before checking tx_free (head and tail) */
+       smp_mb();
+
+       if (c_can_get_tx_free(tx_ring) == 0) {
+               netdev_dbg(priv->dev,
+                          "Stopping tx-queue (tx_head=0x%08x, tx_tail=0x%08x, len=%d).\n",
+                          tx_ring->head, tx_ring->tail,
+                          tx_ring->head - tx_ring->tail);
+               return true;
+       }
+
+       netif_start_queue(priv->dev);
+       return false;
+}
+
 static netdev_tx_t c_can_start_xmit(struct sk_buff *skb,
                                    struct net_device *dev)
 {
        struct can_frame *frame = (struct can_frame *)skb->data;
        struct c_can_priv *priv = netdev_priv(dev);
+       struct c_can_tx_ring *tx_ring = &priv->tx;
        u32 idx, obj;
 
        if (can_dropped_invalid_skb(dev, skb))
                return NETDEV_TX_OK;
-       /* This is not a FIFO. C/D_CAN sends out the buffers
-        * prioritized. The lowest buffer number wins.
-        */
-       idx = fls(atomic_read(&priv->tx_active));
-       obj = idx + priv->msg_obj_tx_first;
 
-       /* If this is the last buffer, stop the xmit queue */
-       if (idx == priv->msg_obj_tx_num - 1)
+       if (c_can_tx_busy(priv, tx_ring))
+               return NETDEV_TX_BUSY;
+
+       idx = c_can_get_tx_head(tx_ring);
+       tx_ring->head++;
+       if (c_can_get_tx_free(tx_ring) == 0)
                netif_stop_queue(dev);
+
+       obj = idx + priv->msg_obj_tx_first;
+
        /* Store the message in the interface so we can call
         * can_put_echo_skb(). We must do this before we enable
         * transmit as we might race against do_tx().
@@ -453,8 +479,6 @@ static netdev_tx_t c_can_start_xmit(struct sk_buff *skb,
        priv->dlc[idx] = frame->len;
        can_put_echo_skb(skb, dev, idx, 0);
 
-       /* Update the active bits */
-       atomic_add(BIT(idx), &priv->tx_active);
        /* Start transmission */
        c_can_object_put(dev, IF_TX, obj, IF_COMM_TX);
 
@@ -567,6 +591,7 @@ static int c_can_software_reset(struct net_device *dev)
 static int c_can_chip_config(struct net_device *dev)
 {
        struct c_can_priv *priv = netdev_priv(dev);
+       struct c_can_tx_ring *tx_ring = &priv->tx;
        int err;
 
        err = c_can_software_reset(dev);
@@ -598,7 +623,8 @@ static int c_can_chip_config(struct net_device *dev)
        priv->write_reg(priv, C_CAN_STS_REG, LEC_UNUSED);
 
        /* Clear all internal status */
-       atomic_set(&priv->tx_active, 0);
+       tx_ring->head = 0;
+       tx_ring->tail = 0;
        priv->tx_dir = 0;
 
        /* set bittiming params */
@@ -696,14 +722,14 @@ static int c_can_get_berr_counter(const struct net_device *dev,
 static void c_can_do_tx(struct net_device *dev)
 {
        struct c_can_priv *priv = netdev_priv(dev);
+       struct c_can_tx_ring *tx_ring = &priv->tx;
        struct net_device_stats *stats = &dev->stats;
-       u32 idx, obj, pkts = 0, bytes = 0, pend, clr;
+       u32 idx, obj, pkts = 0, bytes = 0, pend;
 
        if (priv->msg_obj_tx_last > 32)
                pend = priv->read_reg32(priv, C_CAN_INTPND3_REG);
        else
                pend = priv->read_reg(priv, C_CAN_INTPND2_REG);
-       clr = pend;
 
        while ((idx = ffs(pend))) {
                idx--;
@@ -723,11 +749,14 @@ static void c_can_do_tx(struct net_device *dev)
        if (!pkts)
                return;
 
-       /* Clear the bits in the tx_active mask */
-       atomic_sub(clr, &priv->tx_active);
-
-       if (clr & BIT(priv->msg_obj_tx_num - 1))
-               netif_wake_queue(dev);
+       tx_ring->tail += pkts;
+       if (c_can_get_tx_free(tx_ring)) {
+               /* Make sure that anybody stopping the queue after
+                * this sees the new tx_ring->tail.
+                */
+               smp_mb();
+               netif_wake_queue(priv->dev);
+       }
 
        stats->tx_bytes += bytes;
        stats->tx_packets += pkts;
@@ -1208,6 +1237,10 @@ struct net_device *alloc_c_can_dev(int msg_obj_num)
        priv->msg_obj_tx_last =
                priv->msg_obj_tx_first + priv->msg_obj_tx_num - 1;
 
+       priv->tx.head = 0;
+       priv->tx.tail = 0;
+       priv->tx.obj_num = msg_obj_tx_num;
+
        netif_napi_add(dev, &priv->napi, c_can_poll, priv->msg_obj_rx_num);
 
        priv->dev = dev;