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.
Link: https://lore.kernel.org/r/20210807130800.5246-5-dariobin@libero.it
Suggested-by: Gianluca Falavigna <gianluca.falavigna@inwind.it>
Signed-off-by: Dario Binacchi <dariobin@libero.it>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
The c_can_poll() handles RX/TX events unconditionally. It may therefore
happen that c_can_do_tx() is called unnecessarily because the interrupt
was triggered by the reception of a frame. In these cases, we avoid to
execute unnecessary statements and exit immediately.
Link: https://lore.kernel.org/r/20210807130800.5246-3-dariobin@libero.it
Signed-off-by: Dario Binacchi <dariobin@libero.it>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
The C_CAN/D_CAN cores implement 2 interfaces to manage the message
objects. To avoid concurrency and the need for locking one interface
is used in the TX path (IF_TX). While the other one, named IF_RX is
used from NAPI context only. As this interface is not only used to
manage RX, but also TX message objects, this patch renames IF_RX to
IF_NAPI.
Link: https://lore.kernel.org/r/20210809080608.171545-1-mkl@pengutronix.de
Cc: Dario Binacchi <dariobin@libero.it>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
