linux-kernel - Re: [PATCH] iio: chemical: atlas-sensor: Avoid using irq

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Date:   Thu, 24 Jun 2021 13:13:47 +0200
From:   Nicolas Saenz Julienne <nsaenzju@...hat.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        linux-iio <linux-iio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Matt Ranostay <matt.ranostay@...sulko.com>
Subject: Re: [PATCH] iio: chemical: atlas-sensor: Avoid using irq_work

Hi Andy, thanks for the review.

On Thu, 2021-06-24 at 13:39 +0300, Andy Shevchenko wrote:
> On Thu, Jun 24, 2021 at 1:01 PM Nicolas Saenz Julienne
> <nsaenzju@...hat.com> wrote:
> > 
> > The atlas sensor driver currently registers a threaded IRQ handler whose
> > sole responsibility is to trigger an irq_work which will in turn run
> > iio_trigger_poll() in IRQ context.
> > 
> > This seems overkill given the fact that there already was a opportunity
> 
> an opportunity

Thanks, noted.

> > @@ -474,7 +465,7 @@ static irqreturn_t atlas_interrupt_handler(int irq, void *private)
> >         struct iio_dev *indio_dev = private;
> >         struct atlas_data *data = iio_priv(indio_dev);
> > 
> > -       irq_work_queue(&data->work);
> > +       iio_trigger_poll(data->trig);
> 
> Have you considered dropping atlas_interrupt_trigger_ops() altogether?

Not really, but it makes sense as a separate patch. I'll take care of it.

> 
> >         if (client->irq > 0) {
> >                 /* interrupt pin toggles on new conversion */
> >                 ret = devm_request_threaded_irq(&client->dev, client->irq,
> 
> > -                               NULL, atlas_interrupt_handler,
> > +                               atlas_interrupt_handler, NULL,
> 
> So, you move it from threaded IRQ to be a hard IRQ handler (we have a
> separate call for this).

Noted.

> Can you guarantee that handling of those events will be fast enough?

Do you mean the events triggered in iio_trigger_poll()? If so the amount of
time spent in IRQ context is going to be the same regardless of whether it's
handled through atlas' IRQ or later in irq_work IPI (or softirq context on some
weird platforms).

-- 
Nicolás Sáenz