Re: mcf5441x: flexcan FIFO and mailbox mode (was: Re: [PATCH v5 5/5] can: flexcan: add mcf5441x support)

[Marc Kleine-Budde <mkl@pengutronix.de>]

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On 19.01.2022 07:25:21, Angelo Dureghello wrote:
> > we're currently discussing the option that the user of a flexcan can
> > switch between RX-FIFO and RX via mailboxes.
> > 
> > I noticed that the mcf5441x currently is configured for FIFO mode. Have
> > you tested the driver in mailbox mode?
> > 
> > The reason that some cores use the FIFO mode is, that they cannot
> > receive RTR CAN frames in mailbox mode. According to the IP core
> > overview table, the mcf5441x can receive RTR frames.
> > 
> > If the IP core supports reception of RTR frames, mailbox mode should be
> > used, as it makes use of more buffers (16-2) instead of 6 in FIFO mode.
> > Should we activate mailbox mode for the mcf5441x?
> 
> Ok, not sure why i selected FIFO mode initially, my application
> actually is quite simple. Will try the switch to mailbox, sure,
> looking into this.

Thanks for coming back to me. The mailbox mode performs better under
heavy load, as you have more buffers available. 

If you're using a recent kernel, the flexcan driver has been moved to:
| drivers/net/can/flexcan/flexcan-core.c

diff --git a/drivers/net/can/flexcan/flexcan-core.c b/drivers/net/can/flexcan/flexcan-core.c
index 0bff1884d5cc..aa0b7efb5ca6 100644
--- a/drivers/net/can/flexcan/flexcan-core.c
+++ b/drivers/net/can/flexcan/flexcan-core.c
@@ -296,7 +296,8 @@ static_assert(sizeof(struct flexcan_regs) ==  0x4 * 18 + 0xfb8);
 static const struct flexcan_devtype_data fsl_mcf5441x_devtype_data = {
        .quirks = FLEXCAN_QUIRK_BROKEN_PERR_STATE |
                FLEXCAN_QUIRK_NR_IRQ_3 | FLEXCAN_QUIRK_NR_MB_16 |
-               FLEXCAN_QUIRK_SUPPPORT_RX_FIFO,
+               FLEXCAN_QUIRK_SUPPPORT_RX_MAILBOX |
+               FLEXCAN_QUIRK_SUPPPORT_RX_MAILBOX_RTR,
 };

On older kernel with drivers/net/can/flexcan.c you need:

diff --git a/drivers/net/can/flexcan.c b/drivers/net/can/flexcan.c
index 7734229aa078..538b26619460 100644
--- a/drivers/net/can/flexcan.c
+++ b/drivers/net/can/flexcan.c
@@ -382,7 +382,8 @@ struct flexcan_priv {
 
 static const struct flexcan_devtype_data fsl_mcf5441x_devtype_data = {
        .quirks = FLEXCAN_QUIRK_BROKEN_PERR_STATE |
-               FLEXCAN_QUIRK_NR_IRQ_3 | FLEXCAN_QUIRK_NR_MB_16,
+               FLEXCAN_QUIRK_NR_IRQ_3 | FLEXCAN_QUIRK_NR_MB_16 |
+               FLEXCAN_QUIRK_USE_OFF_TIMESTAMP,
 };
 
 static const struct flexcan_devtype_data fsl_p1010_devtype_data = {

Please apply appropriate change and check if the driver still works if
you RX with full CAN bus load. Please also test if you can still receive
RTR frames.

regards,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |

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