linux-kernel - Re: [PATCH v3] iio: light: ltr390: Implement runtime PM support

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Message-ID: <CAHp75Vcitq5+fJJMKFGC9Qsqe8yAuoxK99YohR8N9218iR_Ocw@mail.gmail.com>
Date: Sat, 30 Aug 2025 17:46:20 +0300
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Akshay Jindal <akshayaj.lkd@...il.com>
Cc: anshulusr@...il.com, jic23@...nel.org, dlechner@...libre.com, 
	nuno.sa@...log.com, andy@...nel.org, shuah@...nel.org, 
	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] iio: light: ltr390: Implement runtime PM support

On Sat, Aug 30, 2025 at 4:24 PM Akshay Jindal <akshayaj.lkd@...il.com> wrote:
> On Sat, Aug 30, 2025 at 6:04 PM Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
> > On Sat, Aug 30, 2025 at 2:35 PM Akshay Jindal <akshayaj.lkd@...il.com> wrote:

...

> > > +static int ltr390_write_event_config(struct iio_dev *indio_dev,
> > > +                               const struct iio_chan_spec *chan,
> > > +                               enum iio_event_type type,
> > > +                               enum iio_event_direction dir,
> > > +                               bool state)
> > > +{
> > > +       int ret;
> > > +       struct ltr390_data *data = iio_priv(indio_dev);
> > > +       struct device *dev = &data->client->dev;
> > > +
> > > +       guard(mutex)(&data->lock);
> > > +
> > > +       if (state && !data->irq_enabled) {
> > > +               ret = pm_runtime_resume_and_get(dev);
> > > +               if (ret < 0) {
> > > +                       dev_err(dev, "runtime PM failed to resume: %d\n", ret);
> > > +                       return ret;
> > > +               }
> > > +               data->irq_enabled = true;
> > > +       }
> > > +
> > > +       ret = __ltr390_write_event_config(indio_dev, chan, type, dir, state);
> > > +
> > > +       if (!state && data->irq_enabled) {
> > > +               data->irq_enabled = false;
> > > +               pm_runtime_put_autosuspend(dev);
> > > +       }
> > > +
> > > +       return ret;
> > > +}
> >
> > This looks like overcomplicated and duplicate checks. Just make two
> > functions with and without IRQ enabling handling.
> >
> LTR390 only supports 1 event/interrupt which is toggled in this callback based
> on value provided to sysfs entry. There cannot be a version of this without IRQ
> handling. It is supposed to do IRQ handling only.
>
> Pseudo code of the said function will be something as follows:
> ltr390_write_event_config() {
> if (interrupt needs to be enabled && previously it was disabled)
>      pm_runtime_resume_and_get()
> do_actual_reg_writes()
> if (interrupt needs to be disabled && previously it was enabled)
>     pm_runtime_put_autosuspend().
> }

I see now, yeah, this is unfortunate.
Just rename the leading __ to the _unlocked() suffix. It's easier to read.

> With the current function , we achieve the following objectives:
> 1. idempotency in refcount change. Meaning if IRQ is already enabled and
> if someone enables it again, it will not increase the refcount, same goes for
> double disable case. This has been tested as well.
> 2. Only if the new and previous config is different, then only the refcount will
> change.
> 3. Adheres to previous comments received regarding checking return value
> of _get and ignoring that of _put.
>
> I genuinely don't see any duplicate checks here. In addition, I feel the above
> function is fine from a simplification point of view and cannot be bifurcated
> further.

You are right I missed the asymmetric conditionals.

> Although, if you could clarify what you mean by further bifurcation, I might be
> able to connect with your thoughts.

-- 
With Best Regards,
Andy Shevchenko