Re: API to support hardware priorities

[Benedikt Spranger <b.spranger@linutronix.de>]

On Mon, 9 Nov 2015 14:51:32 +0100
Marc Kleine-Budde <mkl@pengutronix.de> wrote:

> Are we talking about RX or TX here?
TX.

> Do you mean the mailbox feature, where you queue a frame into
> hardware, but sending is delayed until a certain CAN-ID is RX'ed?
No.
The C-CAN/D-CAN and some other Controller can be configured to have
mailboxes for a certain Id. For example you can configure MBX 1 for
Id 23, MBX 2 for Id 42 and 3-7 act as FIFO. So every packet matching Id
23 should queued up to MBX 1, every package matching Id 42 to MBX 2 and
all other Packages to the FIFO.

Having a multiqueue TX part may help but may have some drawbacks. If the
FIFO (or an other queue) is full the driver calls netif_stop_queue().
Sending bulk data can block out a "high priority" Package. On the other
hand a application writing bulk data in blocking mode should not
receive a EAGAIN and not be punished by a "mixed up" queue i.e.
violating the package send order.

Regards
    Bene

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