can: ti_hecc: use timestamp based rx-offloading

can: ti_hecc: use timestamp based rx-offloading

As already mentioned in [1] and included in [2], there is an off by one
issue since the high bank is already enabled when the _next_ mailbox to
be read has index 12, so the mailbox being read was 13. The message can
therefore go into mailbox 31 and the driver will be repolled until the
mailbox 12 eventually receives a msg. Or the message might end up in the
12th mailbox, but then it would become disabled after reading it and only
be enabled again in the next "round" after mailbox 13 was read, which can
cause out of order messages, since the lower priority mailboxes can
accept messages in the meantime.

As mentioned in [3] there is a hardware race condition when changing the
CANME register while messages are being received. Even when including a
busy poll on reception, like in [2] there are still overflows and out of
order messages at times, but less then without the busy loop polling.
Unlike what the patch suggests, the polling time is not in the microsecond
range, but takes as long as a current CAN bus reception needs to finish,
so typically more in the fraction of millisecond range. Since the timeout
is in jiffies it won't timeout.

Even with these additional fixes the driver is still not able to provide a
proper FIFO which doesn't drop packages. So change the driver to use
rx-offload and base order on timestamp instead of message box numbers. As
a side affect, this also fixes [4] and [5].

Before this change messages with a single byte counter were dropped /
received out of order at a bitrate of 250kbit/s on an am3517. With this
patch that no longer occurs up to and including 1Mbit/s.

[1] https://linux-can.vger.kernel.narkive.com/zgO9inVi/patch-can-ti-hecc-fix-rx-wrong-sequence-issue#post6
[2] http://arago-project.org/git/projects/?p=linux-omap3.git;a=commit;h=02346892777f07245de4d5af692513ebd852dcb2
[3] https://linux-can.vger.kernel.narkive.com/zgO9inVi/patch-can-ti-hecc-fix-rx-wrong-sequence-issue#post5
[4] https://patchwork.ozlabs.org/patch/895956/
[5] https://www.spinics.net/lists/netdev/msg494971.html

Cc: Anant Gole <anantgole@ti.com>
Cc: AnilKumar Ch <anilkumar@ti.com>
Signed-off-by: Jeroen Hofstee <jhofstee@victronenergy.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>