[PATCH v2 13/18] can: m_can: Cache tx putidx

[Markus Schneider-Pargmann <msp@baylibre.com>]

m_can_tx_handler is the only place where data is written to the tx fifo.
We can calculate the putidx in the driver code here to avoid the
dependency on the txfqs register.

Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
---
 drivers/net/can/m_can/m_can.c | 8 +++++++-
 drivers/net/can/m_can/m_can.h | 3 +++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c
index 9d2345f52ddc..83ffb4c0eb4c 100644
--- a/drivers/net/can/m_can/m_can.c
+++ b/drivers/net/can/m_can/m_can.c
@@ -1475,6 +1475,10 @@ static int m_can_start(struct net_device *dev)
 
 	m_can_enable_all_interrupts(cdev);
 
+	if (cdev->version > 30)
+		cdev->tx_fifo_putidx = FIELD_GET(TXFQS_TFQPI_MASK,
+						 m_can_read(cdev, M_CAN_TXFQS));
+
 	return 0;
 }
 
@@ -1764,7 +1768,7 @@ static netdev_tx_t m_can_tx_handler(struct m_can_classdev *cdev)
 		}
 
 		/* get put index for frame */
-		putidx = FIELD_GET(TXFQS_TFQPI_MASK, txfqs);
+		putidx = cdev->tx_fifo_putidx;
 
 		/* Construct DLC Field, with CAN-FD configuration.
 		 * Use the put index of the fifo as the message marker,
@@ -1797,6 +1801,8 @@ static netdev_tx_t m_can_tx_handler(struct m_can_classdev *cdev)
 
 		/* Enable TX FIFO element to start transfer  */
 		m_can_write(cdev, M_CAN_TXBAR, (1 << putidx));
+		cdev->tx_fifo_putidx = (++cdev->tx_fifo_putidx >= cdev->can.echo_skb_max ?
+					0 : cdev->tx_fifo_putidx);
 
 		/* stop network queue if fifo full */
 		if (m_can_tx_fifo_full(cdev) ||
diff --git a/drivers/net/can/m_can/m_can.h b/drivers/net/can/m_can/m_can.h
index 0721faae7886..4437085f63b8 100644
--- a/drivers/net/can/m_can/m_can.h
+++ b/drivers/net/can/m_can/m_can.h
@@ -102,6 +102,9 @@ struct m_can_classdev {
 	u32 tx_max_coalesced_frames_irq;
 	u32 tx_coalesce_usecs_irq;
 
+	// Store this internally to avoid fetch delays on peripheral chips
+	int tx_fifo_putidx;
+
 	struct mram_cfg mcfg[MRAM_CFG_NUM];
 };
 
-- 
2.39.0