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

[Angelo Dureghello <angelo@kernel-space.org>]

Hi Marc,

On Fri, 21 Jan 2022, Marc Kleine-Budde wrote:

> On 21.01.2022 00:35:43, Angelo Dureghello wrote:
>>> 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.
>>>
>>
>> I tested this patch:
>>
>> -------------------- drivers/net/can/flexcan/flexcan-core.c index
>> 0bff1884d5cc..daeeb6250347 100644
>> @@ -296,7 +296,10 @@ 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_USE_RX_MAILBOX |
>> +		FLEXCAN_QUIRK_SUPPPORT_RX_FIFO |
>> +		FLEXCAN_QUIRK_SUPPPORT_RX_MAILBOX |
>> +		FLEXCAN_QUIRK_SUPPPORT_RX_MAILBOX_RTR,
>>  };
>>
>>  static const struct flexcan_devtype_data fsl_p1010_devtype_data = {
>>
>> Bus load PC -> mcf5441x tested by
>>
>> ip link set can0 type can bitrate 1000000
>> ip link set can0 up
>> cangen can0 -g 0
>>
>> On target (mcf54415)
>> candump can0
>>
>> It works, even better then FIFO mode.
>
> What's the difference, does it produce less overruns?
>

In FIFO mode, i had a conditions where the mcf system
was stuck. Had to reboot. Not clear what's happen btw, should try to 
reproduce this.

>> While unfortunately, RTR rx does not work. Tested it by putting
>> a trace in flexcan_mailbox_read()
>>
>> 	if (reg_ctrl & FLEXCAN_MB_CNT_RTR) {
>> 		printk("%s() RX RTR frame\n", __func__);
>> 		cfd->can_id |= CAN_RTR_FLAG;
>> 	}
>>
>> on host pc i used:
>>
>> cangen can0 -R
>>
>> No sign of RTR in rx. While in FIFO mode i can see it.
>
> Ok, then I enable the mailbox support for the mcf5441x and fix the note
> that the IP core doesn't support RTR reception via mailboxes. See the
> following patch:
>
> | https://lore.kernel.org/all/20220121084425.3141218-1-mkl@pengutronix.de
>
> If you have time, please test and add your Tested-by.
>
> You can switch to mailbox mode during runtime, if the interface is down:
>
> | ethtool --set-priv-flags can0 rx-rtr off
>
> With ethtool you can query the number of used RX and TX buffers:
>
> | ethtool --show-ring can0
>
> The FIFO mode uses 6 RX buffers, while mailbox mode will probably use
> 14.
>

My mcf5441x small system does not have ethtool available
right now. Will test this as soon as i can.

> regards,
> Marc

regards,
angelo
>
> -- 
> Pengutronix e.K.                 | Marc Kleine-Budde           |
> Embedded Linux                   | https://www.pengutronix.de  |
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>