Date:   Mon, 1 May 2017 01:22:52 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Eva Rachel Retuya <eraretuya@...il.com>, linux-iio@...r.kernel.org
Cc:     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 29/04/17 08:48, Eva Rachel Retuya wrote:
> Move code that enables measurement/standby mode into its own function
> and call that function when appropriate. Previously, we set the sensor
> to measurement in probe and back to standby during remove. Change it
> here to only enter measurement mode when request for data is initiated.
> 
> The DATA_READY bit is always set if the corresponding event occurs.
> Introduce the data_ready function that monitors the INT_SOURCE register
> of this bit. This is done to ensure consistent readings.
> 
> Signed-off-by: Eva Rachel Retuya <eraretuya@...il.com>
> ---
> Changes in v2:
> * Make function naming more clear: drdy -> data_ready
>   * Switch from while to do..while
>   * Rename regval to val
>   * Switch to usleep_range() for shorter delay
>   * Add comment to justify delay
>   * Change error code -EIO to -EAGAIN
> * Endianness issue: scrap the get_triple function entirely, make no
>   changes in terms of reading registers in read_raw
> * Introduce mutex here rather than in succeeding patch
> * Probe:
>   * Fix random whitespace omission
>   * Remove configuring to standby mode, the device powers on in standby
>     mode so this is not needed
> 
>  drivers/iio/accel/adxl345_core.c | 84 +++++++++++++++++++++++++++++++++-------
>  1 file changed, 69 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/iio/accel/adxl345_core.c b/drivers/iio/accel/adxl345_core.c
> index 9ccb582..b8a212c 100644
> --- a/drivers/iio/accel/adxl345_core.c
> +++ b/drivers/iio/accel/adxl345_core.c
> @@ -8,6 +8,7 @@
>   * directory of this archive for more details.
>   */
>  
> +#include <linux/delay.h>
>  #include <linux/module.h>
>  #include <linux/regmap.h>
>  
> @@ -17,6 +18,7 @@
>  
>  #define ADXL345_REG_DEVID		0x00
>  #define ADXL345_REG_POWER_CTL		0x2D
> +#define ADXL345_REG_INT_SOURCE		0x30
>  #define ADXL345_REG_DATA_FORMAT		0x31
>  #define ADXL345_REG_DATAX0		0x32
>  #define ADXL345_REG_DATAY0		0x34
> @@ -25,6 +27,10 @@
>  #define ADXL345_POWER_CTL_MEASURE	BIT(3)
>  #define ADXL345_POWER_CTL_STANDBY	0x00
>  
> +/* INT_ENABLE/INT_MAP/INT_SOURCE bits */
> +#define ADXL345_INT_DATA_READY		BIT(7)
> +#define ADXL345_INT_OVERRUN		0
> +
>  #define ADXL345_DATA_FORMAT_FULL_RES	BIT(3) /* Up to 13-bits resolution */
>  #define ADXL345_DATA_FORMAT_2G		0
>  #define ADXL345_DATA_FORMAT_4G		1
> @@ -44,9 +50,49 @@ static const int adxl345_uscale = 38300;
>  
>  struct adxl345_data {
>  	struct regmap *regmap;
> +	struct mutex lock; /* protect this data structure */
>  	u8 data_range;
>  };
>  
> +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.
> +	}
> +
> +	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.
> +	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?

> +
> +		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.
> +	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!
> +			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;
> @@ -136,6 +200,8 @@ int adxl345_core_probe(struct device *dev, struct regmap *regmap,
>  		return ret;
>  	}
>  
> +	mutex_init(&data->lock);
> +
>  	indio_dev->dev.parent = dev;
>  	indio_dev->name = name;
>  	indio_dev->info = &adxl345_info;
> @@ -143,20 +209,9 @@ int adxl345_core_probe(struct device *dev, struct regmap *regmap,
>  	indio_dev->channels = adxl345_channels;
>  	indio_dev->num_channels = ARRAY_SIZE(adxl345_channels);
>  
> -	/* Enable measurement mode */
> -	ret = regmap_write(data->regmap, ADXL345_REG_POWER_CTL,
> -			   ADXL345_POWER_CTL_MEASURE);
> -	if (ret < 0) {
> -		dev_err(dev, "Failed to enable measurement mode: %d\n", ret);
> -		return ret;
> -	}
> -
>  	ret = iio_device_register(indio_dev);
> -	if (ret < 0) {
> +	if (ret < 0)
>  		dev_err(dev, "iio_device_register failed: %d\n", ret);
> -		regmap_write(data->regmap, ADXL345_REG_POWER_CTL,
> -			     ADXL345_POWER_CTL_STANDBY);
> -	}
>  
>  	return ret;
>  }
> @@ -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.
>  }
>  EXPORT_SYMBOL_GPL(adxl345_core_remove);
>  
> 

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