linux-kernel - Re: [PATCH v2 2/4] iio: accel: adxl345_core: Introduce set_mode and data

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Message-ID: <20170502113902.GA3030@Socrates-UM>
Date:   Tue, 2 May 2017 19:39:03 +0800
From:   Eva Rachel Retuya <eraretuya@...il.com>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     linux-iio@...r.kernel.org, knaack.h@....de, lars@...afoo.de,
        pmeerw@...erw.net, dmitry.torokhov@...il.com,
        michael.hennerich@...log.com, daniel.baluta@...il.com,
        amsfield22@...il.com, florian.vaussard@...g-vd.ch,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/4] iio: accel: adxl345_core: Introduce set_mode and
 data_ready functions

On Mon, May 01, 2017 at 01:22:52AM +0100, Jonathan Cameron wrote:
Hello Jonathan,
[...]
> > +static int adxl345_set_mode(struct adxl345_data *data, u8 mode)
> > +{
> > +	struct device *dev = regmap_get_device(data->regmap);
> > +	int ret;
> > +
> > +	ret = regmap_write(data->regmap, ADXL345_REG_POWER_CTL, mode);
> > +	if (ret < 0) {
> > +		dev_err(dev, "Failed to set power mode, %d\n", ret);
> > +		return ret;
> drop the return ret here and just return ret at the end of the function.
> One of the static checkers will probably moan about this otherwise.

OK.

> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static int adxl345_data_ready(struct adxl345_data *data)
> > +{
> So this is a polling the dataready bit.  Will ensure we always
> get fresh data when a read occurs.  Please add a comment to
> that effect as that's not always how devices work.

OK.

> > +	struct device *dev = regmap_get_device(data->regmap);
> > +	int tries = 5;
> > +	u32 val;
> > +	int ret;
> > +
> > +	do {
> > +		/*
> > +		 * 1/ODR + 1.1ms; 11.1ms at ODR of 0.10 Hz
> > +		 * Sensor currently operates at default ODR of 100 Hz
> > +		 */
> > +		usleep_range(1100, 11100);
> That's a huge range to allow... I'm not following the argument for why.
> Or do we have a stray 0?
> 

Not a stray 0. Range is from 1.1ms to 11.1ms, this represents the
wake-up time when going to standby/other power saving modes ->
measurement mode. I'm going to clarify the comment on why it is needed
on the next revision.

> > +
> > +		ret = regmap_read(data->regmap, ADXL345_REG_INT_SOURCE, &val);
> > +		if (ret < 0)
> > +			return ret;
> > +		if ((val & ADXL345_INT_DATA_READY) == ADXL345_INT_DATA_READY)
> > +			return 0;
> > +	} while (--tries);
> > +	dev_err(dev, "Data is not yet ready, try again.\n");
> > +
> This is almost certainly a hardware fault. I'd be more brutal with
> the error and return -EIO.  If you get here your hardware is very unlikely
> to be working correctly if you try again.

OK, will change it to -EIO then.

> > +	return -EAGAIN;
> > +}
> > +
> >  #define ADXL345_CHANNEL(reg, axis) {					\
> >  	.type = IIO_ACCEL,						\
> >  	.modified = 1,							\
> > @@ -72,6 +118,19 @@ static int adxl345_read_raw(struct iio_dev *indio_dev,
> >  
> >  	switch (mask) {
> >  	case IIO_CHAN_INFO_RAW:
> > +		mutex_lock(&data->lock);
> > +		ret = adxl345_set_mode(data, ADXL345_POWER_CTL_MEASURE);
> > +		if (ret < 0) {
> > +			mutex_unlock(&data->lock);
> > +			return ret;
> > +		}
> > +
> > +		ret = adxl345_data_ready(data);
> > +		if (ret < 0) {
> > +			adxl345_set_mode(data, ADXL345_POWER_CTL_STANDBY);
> > +			mutex_unlock(&data->lock);
> What is the logic that puts the mutex_unlock here in the error case
> and before the set_mode in the normal path?  Even if it doesn't
> matter make them the same as it is less likely to raise questions
> in the future!

OK, will make it consistent.

> > +			return ret;
> > +		}
> >  		/*
> >  		 * Data is stored in adjacent registers:
> >  		 * ADXL345_REG_DATA(X0/Y0/Z0) contain the least significant byte
> > @@ -79,10 +138,15 @@ static int adxl345_read_raw(struct iio_dev *indio_dev,
> >  		 */
> >  		ret = regmap_bulk_read(data->regmap, chan->address, &regval,
> >  				       sizeof(regval));
> > -		if (ret < 0)
> > +		mutex_unlock(&data->lock);
> > +		if (ret < 0) {
> > +			adxl345_set_mode(data, ADXL345_POWER_CTL_STANDBY);
> >  			return ret;
> > +		}
> >  
> >  		*val = sign_extend32(le16_to_cpu(regval), 12);
> > +		adxl345_set_mode(data, ADXL345_POWER_CTL_STANDBY);
> > +
> >  		return IIO_VAL_INT;
> >  	case IIO_CHAN_INFO_SCALE:
> >  		*val = 0;
[...]
> > @@ -169,8 +224,7 @@ int adxl345_core_remove(struct device *dev)
> >  
> >  	iio_device_unregister(indio_dev);
> >  
> > -	return regmap_write(data->regmap, ADXL345_REG_POWER_CTL,
> > -			    ADXL345_POWER_CTL_STANDBY);
> > +	return adxl345_set_mode(data, ADXL345_POWER_CTL_STANDBY);
> Under what circumstances would we not already be in the correct state?
> A brief comment here would be good.

I'm leaving this unremoved to catch cases where in the sensor fails to
return to standby mode after a read. Will add the said comment.

Thanks,
Eva

> >  }
> >  EXPORT_SYMBOL_GPL(adxl345_core_remove);
> >  
> > 
>