[RESEND PATCH 3/4] can: c_can: support tx ring algorithm

Dario Binacchi
2021-07-25T16:12:10Z

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.

Suggested-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Dario Binacchi <dariobin@libero.it>
---

drivers/net/can/c_can/c_can.h | 19 ++++++-
drivers/net/can/c_can/c_can_main.c | 81 +++++++++++++++++++++++-------
2 files changed, 82 insertions(+), 18 deletions(-)

diff --git a/drivers/net/can/c_can/c_can.h b/drivers/net/can/c_can/c_can.h
index 8f23e9c83c84..8fe7e2138620 100644
--- 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 +226,14 @@ 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);
+}
+
#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 fec0e3416970..451ac9a9586a 100644
--- a/drivers/net/can/c_can/c_can_main.c
+++ b/drivers/net/can/c_can/c_can_main.c
@@ -427,24 +427,64 @@ 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 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;
+}
+
+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 +493,6 @@ 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 +605,7 @@ 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 +637,8 @@ 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 +736,14 @@ 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 +763,14 @@ 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;
@@ -1206,6 +1249,10 @@ 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;
--
2.17.1