Re: [PATCH 0/5] can: mcp251xfd: workaround double-RX erratum

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

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On 11.01.2023 23:20:37, Marc Kleine-Budde wrote:
> this is a proof of concept implementation to work around the
> "double-RX" erratum found by Stefan Althöfer.
> 
> With the help of Thomas we found out that the chip has a time window
> after receiving a CAN frame where the RX FIFO STA register content is
> not read correctly.
> 
> From the driver's point of view, everything looks consistent at first,
> but the head index of the chip is too large. This causes the driver to
> rehandle old CAN frames that have already been processed.
> 
> The workaround uses the RX timestamp to distinguish between new and
> old data. As soon as old data is found, processing is stopped.
> 
> The series applies against current net/main. The patches lack proper
> descriptions, I'll add them in the next round.
> 
> Happy testing,
> Marc
> 
> Link: https://lore.kernel.org/all/FR0P281MB1966273C216630B120ABB6E197E89@FR0P281MB1966.DEUP281.PROD.OUTLOOK.COM

If you add a "#define DEBUG" before any #includes in mcp251xfd-rc.c
you'll get a debug message like this if the workaround triggers:

| Jan 11 22:53:10 riot kernel: mcp251xfd spi1.0 mcp251xfd0: mcp251xfd_handle_rxif_one: last_valid=0x17395fba3d56bb9c ts=0x17395fba3d08ee9e d=0xffffffffffb23302 data=00 02 80 fa 24 cc 43 41 - Dropping

You can also have a look at the interface statistics. The "RX errors:
fifo" is incremented if the workaround triggers.

| $ ip --details -s -s link show mcp251xfd0
| 5: mcp251xfd0: <NOARP,UP,LOWER_UP,ECHO> mtu 72 qdisc pfifo_fast state UP mode DEFAULT group default qlen 10
|     link/can  promiscuity 0 minmtu 0 maxmtu 0 
|     can <LOOPBACK,BERR-REPORTING,FD> state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 1000 
|           bitrate 1000000 sample-point 0.750
|           tq 25 prop-seg 14 phase-seg1 15 phase-seg2 10 sjw 1 brp 1
|           mcp251xfd: tseg1 2..256 tseg2 1..128 sjw 1..128 brp 1..256 brp_inc 1
|           dbitrate 4000000 dsample-point 0.700
|           dtq 25 dprop-seg 3 dphase-seg1 3 dphase-seg2 3 dsjw 1 dbrp 1
|           mcp251xfd: dtseg1 1..32 dtseg2 1..16 dsjw 1..16 dbrp 1..256 dbrp_inc 1
|           clock 40000000 
|           re-started bus-errors arbit-lost error-warn error-pass bus-off
|           0          0          0          0          0          0         numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535 parentbus spi parentdev spi1.0 
|     RX:  bytes packets errors dropped  missed   mcast           
|      190713920 9871978      0       0       0       0 
|     RX errors:  length    crc   frame    fifo overrun           
|                      0      0       0       1       0
                                           ^^^^
|     TX:  bytes packets errors dropped carrier collsns           
|       95356960 4935989      0       0       0       0 
|     TX errors: aborted   fifo  window heartbt transns
|                      0      0       0       0       1 

Note: Certain Out-of-Memory situations also increase the fifo error
counter, but I think you'll get a nice OOM error message from the
kernel, too.

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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