On 13.04.2023 17:30:46, Judith Mendez wrote: > On AM62x there is one MCAN in MAIN domain and two 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. Is this a general hardware limitation, that effects all MCU domain peripherals? Is there a mailbox mechanism between the MCU and the MAIN domain, would it be possible to pass the IRQ with a small firmware on the MCU? Anyways, that's future optimization. > This solution instantiates a hrtimer with 1 ms polling interval > for a MCAN when there is no hardware interrupt. This 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. > > On AM62x this series enables two MCU MCAN which will use the hrtimer > implementation. 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 and lower polling periods than 1ms. Some Linux input drivers have the property poll-interval, would it make sense to ass this here too? > 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. > > This patch series depends on 'Enable CAN PHY transceiver driver': > https://lore.kernel.org/lkml/775ec9ce-7668-429c-a977-6c8995968d6e@xxxxxxxxxxxxxxxx/T/ Marc -- Pengutronix e.K. | Marc Kleine-Budde | Embedded Linux | https://www.pengutronix.de | Vertretung Nürnberg | Phone: +49-5121-206917-129 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-9 |
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