Re: [PATCH v2 4/4] can: c_can: cache frames to operate as a true FIFO

Marc Kleine-Budde
2021-08-06T09:37:08Z

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On 05.08.2021 22:19:00, Dario Binacchi wrote:
> 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 <gianluca.falavigna@inwind.it>
> Signed-off-by: Dario Binacchi <dariobin@libero.it>

My review from
https://lore.kernel.org/linux-can/20210806092523.hij5ejjq6wecbgfr@pengutronix.de/
applies here, too.

Please use IF_RX in c_can_do_tx(), remove the spin_lock and test. After
applying your series, I'll send a patch that changes IF_RX into IF_NAPI
to avoid any further confusion.

regards,
Marc

--
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