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. Letency 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, howerver 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. v7: Link: https://lore.kernel.org/linux-can/20230523023749.4526-1-jm@xxxxxx/T/#t v6: Link: https://lore.kernel.org/linux-can/20230518193613.15185-1-jm@xxxxxx/T/#t v5: Link: https://lore.kernel.org/linux-can/20230510202952.27111-1-jm@xxxxxx/T/#t v4: Link: https://lore.kernel.org/linux-can/c3395692-7dbf-19b2-bd3f-31ba86fa4ac9@xxxxxxxxxx/T/#t v2: Link: https://lore.kernel.org/linux-can/20230424195402.516-1-jm@xxxxxx/T/#t V1: Link: https://lore.kernel.org/linux-can/19d8ae7f-7b74-a869-a818-93b74d106709@xxxxxx/T/#t RFC: Link: https://lore.kernel.org/linux-can/52a37e51-4143-9017-42ee-8d17c67028e3@xxxxxx/T/#t v7: - 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 v6: - 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/798d276b39e984345d52b933a900a71fa0815928 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() Judith Mendez (2): dt-bindings: net: can: Remove interrupt properties for MCAN can: m_can: Add hrtimer to generate software interrupt .../bindings/net/can/bosch,m_can.yaml | 20 +++++++++-- drivers/net/can/m_can/m_can.c | 34 +++++++++++++++++-- drivers/net/can/m_can/m_can.h | 3 ++ drivers/net/can/m_can/m_can_platform.c | 24 +++++++++++-- 4 files changed, 74 insertions(+), 7 deletions(-) base-commit: 798d276b39e984345d52b933a900a71fa0815928 -- 2.34.1
