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

From: Andy Duan <fugang.duan@nxp.com>
To: Jonathan Cameron <Jonathan.Cameron@Huawei.com>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	"maitysanchayan@gmail.com" <maitysanchayan@gmail.com>
Cc: 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>
Subject: RE: [PATCH 1/2] iio: hrtimer-trigger: Mark hrtimer to expire in hard interrupt context
Date: Tue, 22 Sep 2020 02:51:11 +0000	[thread overview]
Message-ID: <AM8PR04MB731594F51648126A764EA066FF3B0@AM8PR04MB7315.eurprd04.prod.outlook.com> (raw)
In-Reply-To: <20200921143206.00006b43@Huawei.com>

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 ?