dev/ic/com.c, callouts and cv_wait

[Brad Spencer <brad%anduin.eldar.org@localhost>]

Hello...

I was wondering if anyone can enlighten me about something I am seeing.

I am working on a driver for the SC16IS7xx family of UART bridges.
These are I2C or SPI devices that provide a 16550 or there abouts
register set that is behind a I2C or SPI bus.  I.E. you can use them to
add more real UARTs to a RPI, via the I2C or SPI bus, for example.

I am reusing the dev/ic/com.c existing code, switching out the cr_read,
cr_write and cr_write_multi functions to calls that speak to the I2C
bus.

This all appears to work as expected:

[   1.0000040] iic0 at bsciic0: I2C bus
[   1.0000040] sc16is7xx0 at iic0 addr 0x48
[   1.0000040] sc16is7xx0: NXP SC16IS750/SC16IS760
[   1.0000040] com1 at sc16is7xx0 channel 0: ns16550a, 16-byte FIFO

The "ns16550a, 16-byte FIFO" came from dev/ic/com.c after it poked the
chip registers so I suspect that those calls to the I2C bus are working
as expected at least for reads.

I am using polling mode with dev/ic/com.c which simulates hardware
interrupts using a callout to com_intr_poll.  When the callout runs and
tries to access the I2C bus I get this panic:

[   2.1213299] panic: kernel diagnostic assertion "(l->l_pflag & LP_INTR) == 0 |
| panicstr != NULL" failed: file "../../../../kern/kern_condvar.c", line 133
[   2.1213299] cpu0: Begin traceback...
[   2.1213299] 0xba581d94: netbsd:db_panic+0x14
[   2.1213299] 0xba581db4: netbsd:vpanic+0x114
[   2.1213299] 0xba581dcc: netbsd:kern_assert+0x40
[   2.1213299] 0xba581e04: netbsd:cv_wait+0x1b0
[   2.1213299] 0xba581e34: netbsd:bsciic_exec+0xb4
[   2.1213299] 0xba581e6c: netbsd:sc16is7xxi2c_read_register_direct+0x74
[   2.1213299] 0xba581e8c: netbsd:sc16is7xx_i2c_com_read_1+0x38
[   2.1213299] 0xba581ecc: netbsd:comintr+0x6c
[   2.1213299] 0xba581ee4: netbsd:com_intr_poll+0x14
[   2.1213299] 0xba581f34: netbsd:callout_softclock+0xe0
[   2.1213299] 0xba581fac: netbsd:softint_dispatch+0x128
[   2.1213299] Bad frame pointer: 0x80cddf54
[   2.1213299] cpu0: End traceback...

That was on a RPI, but the same sort of thing happens with umcpmio(4)
too on a amd64 VM.  In that case it is a cv_wait_sig that panics in the
USB stack.

dev/ic/com.c was adjusted some to allow higher level code to ask that
dev/ic/com.c mutex to run as an adaptive lock instead of IPL_HIGH, its
callouts were declared MPSAFE (ignoring for a moment that they might not
be) and the softint that is used to call comsoft was declared MPSAFE
(also ignoring for a second that it might not be).  These last two
adjustments were mostly to keep the code from using the global kernel
lock.  Its probably incorrect, but I am mostly just trying to get
through attach at this point.

I read the man page for callout a number of times and it does not appear
to hint one way or the other if callout(9) are allowed to cv_wait, but
it seems like they are not.

I have used cv_wait from kernel threads before, but I have never
attempted to do use them from a callout (I don't think).  Did I miss
something, or is this case not allowed??


BTW - as a brief aside if dev/ic/com.c runs with its mutex at IPL_HIGH
and tries to use the I2C bus it doesn't make it past the iic_acquire_bus
as that can sleep and you get the "trying to sleep with a spin lock"
panic.





-- 
Brad Spencer - brad%anduin.eldar.org@localhost