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From: Stefan Agner <stefan@agner.ch>
To: Sanchayan Maity <maitysanchayan@gmail.com>
Cc: Andy Duan <fugang.duan@nxp.com>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Christian Eggers <ceggers@arri.de>,
	Jonathan Cameron <jic23@kernel.org>,
	Lars-Peter Clausen <lars@metafoo.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Hartmut Knaack <knaack.h@gmx.de>,
	Peter Meerwald-Stadler <pmeerw@pmeerw.net>,
	linux-iio@vger.kernel.org
Subject: Re: [PATCH 1/2] iio: hrtimer-trigger: Mark hrtimer to expire in hard interrupt context
Date: Thu, 24 Sep 2020 10:54:39 +0200	[thread overview]
Message-ID: <0861e8406165c4faf6ab0443cc05ffc0@agner.ch> (raw)
In-Reply-To: <20200924064132.GA22507@core-precision>

On 2020-09-24 08:41, Sanchayan Maity wrote:
> On 20-09-22 02:51:11, Andy Duan wrote:
>> 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 ?
>>
> 
> Sorry for the delay in reply. Unfortunately can't as I do not access to the
> hardware having left Toradex.
> 
> CCed Stefan Agner who might be able to help.
> 
> @Stefan
> 
> Hello Stefan :), may be you can help here?

Hi all,

I do have access to the hardware and can run a test if required. I guess
I would just need to test if ADC sampling still work with something like
tools/iio/iio_generic_buffer.c?

--
Stefan

  reply	other threads:[~2020-09-24  9:01 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-13  7:53 [PATCH 1/2] iio: hrtimer-trigger: Mark hrtimer to expire in hard interrupt context Lars-Peter Clausen
2020-08-13  7:53 ` [PATCH 2/2] iio: sysfs-trigger: Mark irq_work to expire in hardirq context Lars-Peter Clausen
2020-08-13  9:11 ` [PATCH 1/2] iio: hrtimer-trigger: Mark hrtimer to expire in hard interrupt context Sebastian Andrzej Siewior
2020-08-13  9:46   ` Lars-Peter Clausen
2020-08-13 11:27     ` Sebastian Andrzej Siewior
2020-08-13 12:19       ` Thomas Gleixner
2020-08-13 14:55         ` Jonathan Cameron
2020-08-14  5:24           ` Lars-Peter Clausen
2020-08-14 10:30             ` Jonathan Cameron
2020-09-20 18:15               ` Jonathan Cameron
2020-09-21  7:17                 ` Christian Eggers
2020-09-21  9:57                   ` Jonathan Cameron
2020-09-21 12:27                     ` Sebastian Andrzej Siewior
2020-09-21 13:32                       ` Jonathan Cameron
2020-09-22  2:51                         ` Andy Duan
2020-09-24  6:41                           ` Sanchayan Maity
2020-09-24  8:54                             ` Stefan Agner [this message]
2020-09-25 12:42                               ` Jonathan Cameron
2020-10-02 14:10                     ` Christian Eggers
2020-10-10 13:23                       ` Jonathan Cameron

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