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

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Date:   Sun, 26 Sep 2021 16:33:38 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Nicolas Saenz Julienne <nsaenzju@...hat.com>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        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

On Thu, 24 Jun 2021 13:13:47 +0200
Nicolas Saenz Julienne <nsaenzju@...hat.com> wrote:

> 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).
> 

Hi Nicolas, Andy, Matt,

Just been checking patchwork for IIO and noted that this one is still outstanding.

My reading of above is that we kind of got to a conclusion - though I'd like
Matt to sanity check the patch (and maybe test it if he still has hardware for
this?)

We have a generic form of this handler that may let you drop the atlas_interrupt_handler()
function entirely iio_trigger_generic_data_rdy_poll().

https://elixir.bootlin.com/linux/latest/source/drivers/iio/industrialio-trigger.c#L182

Thanks,

Jonathan