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

From: Sanchayan Maity <maitysanchayan@gmail.com>
To: Andy Duan <fugang.duan@nxp.com>
Cc: 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" <linux-iio@vger.kernel.org>,
	Stefan Agner <stefan@agner.ch>
Subject: Re: [PATCH 1/2] iio: hrtimer-trigger: Mark hrtimer to expire in hard interrupt context
Date: Thu, 24 Sep 2020 12:11:32 +0530	[thread overview]
Message-ID: <20200924064132.GA22507@core-precision> (raw)
In-Reply-To: <AM8PR04MB731594F51648126A764EA066FF3B0@AM8PR04MB7315.eurprd04.prod.outlook.com>

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?