[PATCH] iio: chemical: atlas-sensor: Avoid using irq_work

[PATCH] iio: chemical: atlas-sensor: Avoid using irq_work

[Nicolas Saenz Julienne]

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
to run iio_trigger_poll() in IRQ context in the top half of the IRQ
handler. So make use of it, ultimately avoiding a context switch, an
IPI, and reducing latency.

Signed-off-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
---

NOTE: This was only compile tested. I don't know much about iio_triggers
(or iio for that matter), but while reviewing irq_work usage this showed
up and seemed trivial enough to fix right away. There might be a subtle
reason why this is setup as such, but it would at least warrant a
comment.

 drivers/iio/chemical/atlas-sensor.c | 15 ++-------------
 1 file changed, 2 insertions(+), 13 deletions(-)

diff --git a/drivers/iio/chemical/atlas-sensor.c b/drivers/iio/chemical/atlas-sensor.c
index 9cb99585b6ff..710daa169d57 100644
--- a/drivers/iio/chemical/atlas-sensor.c
+++ b/drivers/iio/chemical/atlas-sensor.c
@@ -13,7 +13,6 @@
 #include <linux/mutex.h>
 #include <linux/err.h>
 #include <linux/irq.h>
-#include <linux/irq_work.h>
 #include <linux/i2c.h>
 #include <linux/mod_devicetable.h>
 #include <linux/regmap.h>
@@ -89,7 +88,6 @@ struct atlas_data {
 	struct iio_trigger *trig;
 	struct atlas_device *chip;
 	struct regmap *regmap;
-	struct irq_work work;
 	unsigned int interrupt_enabled;
 	/* 96-bit data + 32-bit pad + 64-bit timestamp */
 	__be32 buffer[6] __aligned(8);
@@ -442,13 +440,6 @@ static const struct iio_buffer_setup_ops atlas_buffer_setup_ops = {
 	.predisable = atlas_buffer_predisable,
 };
 
-static void atlas_work_handler(struct irq_work *work)
-{
-	struct atlas_data *data = container_of(work, struct atlas_data, work);
-
-	iio_trigger_poll(data->trig);
-}
-
 static irqreturn_t atlas_trigger_handler(int irq, void *private)
 {
 	struct iio_poll_func *pf = private;
@@ -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);
 
 	return IRQ_HANDLED;
 }
@@ -677,12 +668,10 @@ static int atlas_probe(struct i2c_client *client,
 		goto unregister_trigger;
 	}
 
-	init_irq_work(&data->work, atlas_work_handler);
-
 	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,
 				IRQF_TRIGGER_RISING |
 				IRQF_TRIGGER_FALLING | IRQF_ONESHOT,
 				"atlas_irq",
-- 
2.31.1

Re: [PATCH] iio: chemical: atlas-sensor: Avoid using irq_work

[Andy Shevchenko]

On Thu, Jun 24, 2021 at 1:01 PM Nicolas Saenz Julienne
<nsaenzju@redhat.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

> to run iio_trigger_poll() in IRQ context in the top half of the IRQ
> handler. So make use of it, ultimately avoiding a context switch, an
> IPI, and reducing latency.

...

> @@ -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?

>         return IRQ_HANDLED;

...

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

>                                 IRQF_TRIGGER_RISING |
>                                 IRQF_TRIGGER_FALLING | IRQF_ONESHOT,
>                                 "atlas_irq",


-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH] iio: chemical: atlas-sensor: Avoid using irq_work

[Nicolas Saenz Julienne]

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@redhat.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

Re: [PATCH] iio: chemical: atlas-sensor: Avoid using irq_work

[Jonathan Cameron]

On Thu, 24 Jun 2021 13:13:47 +0200
Nicolas Saenz Julienne <nsaenzju@redhat.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@redhat.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