Re: [RFC: PATCH 2/2] iio: adc: exynos_adc: Handle timeout and race conditions

[Doug Anderson]

On Fri, Mar 15, 2013 at 2:53 PM, Lars-Peter Clausen <lars@xxxxxxxxxx> wrote:
> What exactly is the spinlock protecting against here? Concurrent runs of
> exynos_adc_isr? This is probably not issue in the first place.
>
> What you want to protect against is that completion is completed between the
> call to INIT_COMPLETION() and the start of a new conversion. So the sections
> that need to be under the spinlock are the complete call here and the point
> from INIT_COMPLETION until the transfer is started in exynos_read_raw(). Make
> sure to use spin_lock_irq there.

...and at that point I _think_ you won't also need the mutex.

A reasonable way to test to see if you've got this all correct would be to:

* Start two processes that are reading from different ADCs that will
report very different values (maybe add a device tree node for adc1 or
adc7 and use those since they're not really connected to
thermistors?).

* Have your two processes read as fast as they can.  This could just
be "while true; do cat /sys/class/hwmon/hwmon0/device/temp1_input;
done"

* Decrease your timeout and maybe(?) sprinkle some random udelays in
the irq handler so that the timeouts happen sometimes but not others.

* Periodically cancel one of the readers with Ctrl-C

If all is working well then you should always get back the right value
from the right reader (and get no crashes).

-Doug
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/