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

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Message-ID: <20241208173336.6a09c9b2@jic23-huawei>
Date: Sun, 8 Dec 2024 17:33:36 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Vasileios Amoiridis <vassilisamir@...il.com>, 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 Tue, 3 Dec 2024 14:42:36 +0200
Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:

> 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!
> 
I tweaked it and applied the series to the togreg branch of iio.git and
pushed out as testing for all the normal reasons.

There was some mess because of the EXPORT_SYMBOL() macro changes this raced
against.  Please sanity check I didn't mess it up.

Jonathan