RE: [PATCH 1/2] iio: hrtimer-trigger: Mark hrtimer to expire in hard interrupt context

Andy Duan
2020-09-22T02:51:16Z

From: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
> On Mon, 21 Sep 2020 14:27:28 +0200
> Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:
>
> > On 2020-09-21 10:57:03 [+0100], Jonathan Cameron wrote:
> > > So looking at this the other way, are there any significant risks
> > > associated with this change? If not I'm tempted to queue them up
> > > and we have the rcX time to fix anything we've missed (just like
> > > every other patch!)
> >
> > I've been told that it only performs IRQ-thread wake-ups in hard-IRQ
> > context. This is fine then.
> >
> drivers/iio/adc/vf610-adc.c
>
> However, there looks to be a lot more wrong in there than just this.
> So normally for a device with a data ready signal like this we would hook up as
> follows.
>
> Data ready #1 -> IRQ chip (trigger) -> Read sensor #1 +
> iio_trigger_notify_done()
> -> Read sensor #2 +
> iio_trigger_notify_done()
>
> (note that the read etc is normally in a thread - all we do in interrupt context is
> usually to grab a timestamp if that makes sense for a given sensor).
>
> This driver does both of.
> Data ready -> Read data from itself and call iio_trigger_notify_done() IRQ chip
> for a different trigger -> Take a timestamp and never call
> iio_trigger_notify_done()
> or read any data for that matter.
>
> Which won't do what we want at all.
>
> Andy, if I have a go at fixing this are you able to test the result?
> I think the simplest is probably to introduce a trigger to tie the two halves
> together.
> We can set it as the default trigger so things should keep on working for existing
> users.
>
> For more general case, we should probably have two functions.
>
> iio_trigger_notify_done() which is only called from places we can sleep.
> iio_trigger_notify_done_no_action() which only decrements the counter (or
> given this is only called inside industrialio-trigger.c could just replace with
> atomic_dec(&trig->use_count)).
>

Sanchayan, can you help to verify the fixes that Jonathan will send out ?