Re: [RESEND PATCH 4/4] can: c_can: cache frames to operate as a true FIFO

Hi Marc,

Il 04/08/2021 11:34 Marc Kleine-Budde [off-list ref] ha scritto:

 
On 25.07.2021 18:11:50, Dario Binacchi wrote:

quoted

As reported by a comment in the c_can_start_xmit() this was not a FIFO.
C/D_CAN controller sends out the buffers prioritized so that the lowest
buffer number wins.

What did c_can_start_xmit() do if head was less tail in the tx ring ? It
waited until all the frames queued in the FIFO was actually transmitted
by the controller before accepting a new CAN frame to transmit, even if
the FIFO was not full, to ensure that the messages were transmitted in
the order in which they were loaded.

By storing the frames in the FIFO without requiring its transmission, we
will be able to use the full size of the FIFO even in cases such as the
one described above. The transmission interrupt will trigger their
transmission only when all the messages previously loaded but stored in
less priority positions of the buffers have been transmitted.

Suggested-by: Gianluca Falavigna <redacted>
Signed-off-by: Dario Binacchi <redacted>

---

 drivers/net/can/c_can/c_can.h      |  6 +++++
 drivers/net/can/c_can/c_can_main.c | 42 +++++++++++++++++-------------
 2 files changed, 30 insertions(+), 18 deletions(-)

diff --git a/drivers/net/can/c_can/c_can.h b/drivers/net/can/c_can/c_can.h
index 8fe7e2138620..fc499a70b797 100644
--- a/drivers/net/can/c_can/c_can.h
+++ b/drivers/net/can/c_can/c_can.h
+static inline u8 c_can_get_tx_free(const struct c_can_tx_ring *ring)
+{
+	return ring->obj_num - (ring->head - ring->tail);
+}
+
 #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 451ac9a9586a..4c061fef002c 100644
--- a/drivers/net/can/c_can/c_can_main.c
+++ b/drivers/net/can/c_can/c_can_main.c

@@ -427,20 +427,6 @@ 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 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;
-}
-

Can you move that change into patch 3?

Patch 3 adds the ring transmission algorithm without compromising the
message transmission order. This is not a FIFO. C/D_CAN controller sends
out the buffers prioritized. The lowest buffer number wins, so moving the
change into patch 3 may not guarantee the transmission order.
In patch 3, however, I will move c_can_get_tx_free() from c_can_main.c to 
c_can.h, so that in patch 4 it will be clearer how the routine has changed.

Thanks and regards,
Dario

Marc

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