FlexCAN i.MX28 BUG! hardware recovered automatically from BUS_OFF

FlexCAN i.MX28 BUG! hardware recovered automatically from BUS_OFF

[Stanislav Meduna]

On 07.03.2014 09:08, Stanislav Meduna wrote:
Hi,

I am using a FlexCAN CAN controller on a Freescale i.MX28
platform [1] and I am upgrading from kernel 3.4 to 3.12.15-rt25.
I am testing the behaviour regarding bus errors, so I run
a test program where the can1 sends and can0 receives and
I am trying to induce bus problems.

If there is no ip link set ... restart-ms parametrized,
the bus does not recover from being left unconnected for
a while

# ip -d -s link show can1
3: can1: <NO-CARRIER,NOARP,UP,ECHO> mtu 16 qdisc pfifo_fast state DOWN qlen 10
    link/can
    can state BUS-OFF (berr-counter tx 0 rx 0) restart-ms 0
    bitrate 500000 sample-point 0.875
    tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1
    flexcan: tseg1 4..16 tseg2 2..8 sjw 1..4 brp 1..256 brp-inc 1
    clock 24000000
    re-started bus-errors arbit-lost error-warn error-pass bus-off
    0          0          0          7          3          2
    RX: bytes  packets  errors  dropped overrun mcast
    320        130      0       0       0       0
    TX: bytes  packets  errors  dropped carrier collsns
    117        59       0       1       0       0

If I configure restart-ms 100, the controller recovers

3: can1: <NOARP,UP,LOWER_UP,ECHO> mtu 16 qdisc pfifo_fast state UP qlen 10
    link/can
    can state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 100
    bitrate 500000 sample-point 0.875
    tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1
    flexcan: tseg1 4..16 tseg2 2..8 sjw 1..4 brp 1..256 brp-inc 1
    clock 24000000
    re-started bus-errors arbit-lost error-warn error-pass bus-off
    20         0          0          27         23         22
    RX: bytes  packets  errors  dropped overrun mcast
    960        210      0       0       0       0
    TX: bytes  packets  errors  dropped carrier collsns
    147        73       0       22      0       0

but while disconnected it floods the log with

[ 1866.452038] flexcan 80034000.can can1: writing ctrl=0x0231a055
[ 1867.447723] flexcan 80034000.can can1: BUG! hardware recovered automatically from BUS_OFF
[ 1867.456128] flexcan 80034000.can can1: writing ctrl=0x0231a055
[ 1868.447649] flexcan 80034000.can can1: BUG! hardware recovered automatically from BUS_OFF

Is this the expected behaviour? What exactly is the "BUG"?

Please Cc: me when replying.

[1] http://www.tq-group.com/en/products/product-details/prod/embedded-modul-tqma28/extb/Main/productdetail/

Thanks
-- 
                                              Stano