Merge patch series "Enable multiple MCAN on AM62x"

Judith Mendez <jm@ti.com> says:

On AM62x there are two MCANs in MCU domain. The MCANs in MCU domain
were not enabled since there is no hardware interrupt routed to A53
GIC interrupt controller. Therefore A53 Linux cannot be interrupted by
MCU MCANs.

This solution instantiates a hrtimer with 1 ms polling interval for
MCAN device when there is no hardware interrupt property in DTB MCAN
node. The hrtimer generates a recurring software interrupt which
allows to call the isr. The isr will check if there is pending
transaction by reading a register and proceed normally if there is.
MCANs with hardware interrupt routed to A53 Linux will continue to use
the hardware interrupt as expected.

Timer polling method was tested on both classic CAN and CAN-FD at 125
KBPS, 250 KBPS, 1 MBPS and 2.5 MBPS with 4 MBPS bitrate switching.

Latency and CPU load benchmarks were tested on 3x MCAN on AM62x. 1
MBPS timer polling interval is the better timer polling interval since
it has comparable latency to hardware interrupt with the worse case
being 1ms + CAN frame propagation time and CPU load is not
substantial. Latency can be improved further with less than 1 ms
polling intervals, however it is at the cost of CPU usage since CPU
load increases at 0.5 ms.

Note that in terms of power, enabling MCU MCANs with timer-polling
implementation might have negative impact since we will have to wake
up every 1 ms whether there are CAN packets pending in the RX FIFO or
not. This might prevent the CPU from entering into deeper idle states
for extended periods of time.

v9:
Link: https://lore.kernel.org/linux-can/20230419223323.20384-1-jm@ti.com
v8:
Link: https://lore.kernel.org/linux-can/20230530224820.303619-1-jm@ti.com
v7:
Link: https://lore.kernel.org/linux-can/20230523023749.4526-1-jm@ti.com
v6:
Link: https://lore.kernel.org/linux-can/20230518193613.15185-1-jm@ti.com
v5:
Link: https://lore.kernel.org/linux-can/20230510202952.27111-1-jm@ti.com
v4:
Link: https://lore.kernel.org/linux-can/20230501224624.13866-1-jm@ti.com
v3:
Link: https://lore.kernel.org/linux-can/20230501223121.21663-1-jm@ti.com
v2:
Link: https://lore.kernel.org/linux-can/20230424195402.516-1-jm@ti.com
RFC:
Link: https://lore.kernel.org/linux-can/20230413223051.24455-1-jm@ti.com/
v10:
- set irq=0 during declaration
- return irq error value instead of -EINVAL;

v9:
- Change add MS to HRTIMER_POLL_INTERVAL
- Change syntax from "= 0" to "!"

v8:
- Cancel hrtimer after interrupts in m_can_stop
- Move assignment of hrtimer_callback to m_can_class_register()
- Initialize irq = 0 if polling mode is used

v7:
- Clean up m_can_platform.c after removing poll-interval

v6:
- Move hrtimer stop/start function calls to m_can_open and m_can_close to
  support power suspend/resume

v5:
- Remove poll-interval in bindings
- Change dev_dbg to dev_info if hardware int exists and polling
  is enabled

v4:
- Wrong patches sent

v3:
- Update binding poll-interval description
- Add oneOf to select either
  interrupts

v2:
- Add poll-interval property to bindings and MCAN DTB node
- Add functionality to check for 'poll-interval' property in MCAN node
- Bindings: add an example using poll-interval
- Add 'polling' flag in driver to check if device is using polling method
- Check for timer polling and hardware interrupt cases, default to
  hardware interrupt method
- Change ns_to_ktime() to ms_to_ktime()

Link: https://lore.kernel.org/all/20230707204714.62964-1-jm@ti.com
[mkl: fix typos in merge request, fix links]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>