Raspberry Pi 2 - I2C related kpanic @ r324169

[Hyun Hwang]

On Thu, Nov 16, 2017, at 12:17, Ian Lepore wrote:
> I broke something. :)
Please do not take my message was to blame you; I greatly appreciate what you did to support the repeated start condition on RPi.

> Is it easily reproducible?
This happens quite randomly, but I managed to reproduce it several times more, especially within gdb(1)-ing my application.

>  I don't expect witness to add anything; given the FAR value, it looks like a NULL pointer problem.
With WITNESS (using standard sys/arm/conf/RPI2 kernel configuration), at least the panic gave me the exact instruction as well as additional messages:
```
Kernel page fault with the following non-sleepable locks held:
exclusive sleep mutex bcm_bsc (bcm_bsc) r = 0 (0xc3d2f688) locked @ /usr/src/sys/arm/broadcom/bcm2835/bcm2835_bsc.c:480
stack backtrace:
Fatal kernel mode data abort: 'Translation Fault (L2)' on read
... snip (very similar to the one in the previous message) ...
Stopped at      bcm_bsc_fill_tx_fifo+0x74:      ldrb    r3, [r2]
db>
```
Hope this helps a bit more.

> could you do a "bt" at the db> propmt and paste that output, please?
Unfortunately, when the kernel panics, the USB keyboard stops working so I cannot type anything...
I will try to find other means that can give input to the debugger. (maybe UART serial?)

Thank you.
-- 
Hyun Hwang