linux-kernel - Re: [PATCH v5 3/3] iio: chemical: bme680: add power management

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Message-ID: <Z078vIxRoQf_zLsy@smile.fi.intel.com>
Date: Tue, 3 Dec 2024 14:42:36 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Vasileios Amoiridis <vassilisamir@...il.com>
Cc: jic23@...nel.org, lars@...afoo.de, robh@...nel.org, krzk+dt@...nel.org,
	conor+dt@...nel.org, u.kleine-koenig@...gutronix.de,
	linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 3/3] iio: chemical: bme680: add power management

On Mon, Dec 02, 2024 at 09:35:50PM +0100, Vasileios Amoiridis wrote:
> On Mon, Dec 02, 2024 at 09:43:36PM +0200, Andy Shevchenko wrote:
> > On Mon, Dec 02, 2024 at 08:23:41PM +0100, Vasileios Amoiridis wrote:
> > > Add runtime power management to the device.

...

> > > +	ret = pm_runtime_resume_and_get(dev);
> > > +	if (ret)
> > > +		return ret;
> > > +
> > > +	ret = __bme680_read_raw(indio_dev, chan, val, val2, mask);
> > > +	pm_runtime_mark_last_busy(dev);
> > > +	pm_runtime_put_autosuspend(dev);
> > 
> > Side note: as long as idle method is not defined (NULL) the above dance is
> > already taken into account in the regular put.

> Thanks again for the review! Indeed by looking at the code a bit, it
> looks like the suspend callback is being called if the idle one is not
> found. But I have seen this dance that you mention much more often in
> the IIO that's why I used it. We can see what Jonathan has to say as
> well, I think what you propose, simplifies things.

Yeah, this is cargo cult by many people (including me :-) who missed that
detail. If any, this can be addressed in a different series.

...

> > > +static int bme680_buffer_preenable(struct iio_dev *indio_dev)
> > > +{
> > > +	struct bme680_data *data = iio_priv(indio_dev);
> > > +	struct device *dev = regmap_get_device(data->regmap);
> > > +	int ret;
> > 
> > > +	ret = pm_runtime_resume_and_get(dev);
> > > +	if (ret)
> > > +		return ret;
> > > +
> > > +	return 0;
> > 
> > Either this is broken (if the above can return positive codes), or can be
> > replaced with direct return:
> > 
> > 	return pm_...
> > 
> > (but I believe it's the former and you wanted something like if (ret < 0)
> >  there).
> > 
> > > +}
> 
> Well, pm_runtime_resume_and_get() looks like it returns 0 on success and
> negative value on error so I think the if (ret) is correct, no? But I
> agree with you that it can be simplified as you proposed.

Please, go ahead with the simplification!

-- 
With Best Regards,
Andy Shevchenko