On 18.08.2022 12:30:31, Marc Kleine-Budde wrote:

One step at a time, let's look at the TX path:

On 17.08.2022 16:35:29, Dario Binacchi wrote:

quoted

+static netdev_tx_t bxcan_start_xmit(struct sk_buff *skb,
+				    struct net_device *ndev)
+{
+	struct bxcan_priv *priv = netdev_priv(ndev);
+	struct can_frame *cf = (struct can_frame *)skb->data;
+	struct bxcan_regs *regs = priv->regs;
+	struct bxcan_mb *mb_regs;

__iomem?

quoted

+	unsigned int mb_id;
+	u32 id, tsr;
+	int i, j;
+
+	if (can_dropped_invalid_skb(ndev, skb))
+		return NETDEV_TX_OK;
+
+	tsr = readl(&regs->tsr);
+	mb_id = ffs((tsr & BXCAN_TSR_TME) >> BXCAN_TSR_TME_SHIFT);

We want to send the CAN frames in the exact order they are pushed into
the driver, so don't pick the first free mailbox you find. How a

                                                                 are

priorities for the TX mailboxes handled?

Is the mailbox with the lowest number send first? Is there a priority
field in the mailbox?

I just had a look into the data sheet and it says that the TX mailboxes
are handled in transmit request order. This is good.

[...]

The mcp251xfd has a proper hardware FIFO ring buffer for TX, the bxcan
probably doesn't. The get_tx_free() check is a bit different. Look at
c_can_get_tx_free() in:

This means you can use the simpler get_tx_free from the mcp251xfd driver.

| https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=28e86e9ab522e65b08545e5008d0f1ac5b19dad1

This patch is a good example for the relevant changes.

This patch is non the less a good example for the TX path.

Marc

-- 
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