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>

1 files changed, 32 insertions, 1 deletions

diff --git a/drivers/net/can/c_can/c_can.h b/drivers/net/can/c_can/c_can.h
index 8f23e9c83c84..9b4e54c950a6 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 +226,28 @@ 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 */