Re: [PATCH] iio: hid-sensors: Increase the precision of scale

[Jonathan Cameron <jic23@kernel.org>]

On 25/10/16 02:30, Song Hongyan wrote:
> While testing, it was observed that on some platforms the scale value
> from iio sysfs for gyroscope is always 0 (E.g. Yoga 260). This results
> in the final angular velocity component values to be zeros.
> 
> This is caused by insufficient precision of scale value displayed in sysfs.
> If the precision is changed to nano from current micro, then this is
> sufficient to display the scale value on this platform.
> Since this can be a problem for all other HID sensors, increase scale
> precision of all HID sensors to nano from current micro.
> 
> Results on Yoga 260:
> 
> name		scale before	scale now
> --------------------------------------------
> gyro_3d		0.000000	0.000000174
> als			0.001000	0.001000000
> magn_3d		0.000001	0.000001000
> accel_3d		0.000009	0.000009806
> 
> Signed-off-by: Song Hongyan <hongyan.song@intel.com>
Hi

Looks right to me, Srinivas, I'd like your Ack on this ideally.

thanks,

Jonathan
> ---
>  .../iio/common/hid-sensors/hid-sensor-attributes.c | 56 +++++++++++-----------
>  1 file changed, 28 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/iio/common/hid-sensors/hid-sensor-attributes.c b/drivers/iio/common/hid-sensors/hid-sensor-attributes.c
> index dc33c1d..b5beea53 100644
> --- a/drivers/iio/common/hid-sensors/hid-sensor-attributes.c
> +++ b/drivers/iio/common/hid-sensors/hid-sensor-attributes.c
> @@ -30,26 +30,26 @@
>  	u32 usage_id;
>  	int unit; /* 0 for default others from HID sensor spec */
>  	int scale_val0; /* scale, whole number */
> -	int scale_val1; /* scale, fraction in micros */
> +	int scale_val1; /* scale, fraction in nanos */
>  } unit_conversion[] = {
> -	{HID_USAGE_SENSOR_ACCEL_3D, 0, 9, 806650},
> +	{HID_USAGE_SENSOR_ACCEL_3D, 0, 9, 806650000},
>  	{HID_USAGE_SENSOR_ACCEL_3D,
>  		HID_USAGE_SENSOR_UNITS_METERS_PER_SEC_SQRD, 1, 0},
>  	{HID_USAGE_SENSOR_ACCEL_3D,
> -		HID_USAGE_SENSOR_UNITS_G, 9, 806650},
> +		HID_USAGE_SENSOR_UNITS_G, 9, 806650000},
>  
> -	{HID_USAGE_SENSOR_GYRO_3D, 0, 0, 17453},
> +	{HID_USAGE_SENSOR_GYRO_3D, 0, 0, 17453293},
>  	{HID_USAGE_SENSOR_GYRO_3D,
>  		HID_USAGE_SENSOR_UNITS_RADIANS_PER_SECOND, 1, 0},
>  	{HID_USAGE_SENSOR_GYRO_3D,
> -		HID_USAGE_SENSOR_UNITS_DEGREES_PER_SECOND, 0, 17453},
> +		HID_USAGE_SENSOR_UNITS_DEGREES_PER_SECOND, 0, 17453293},
>  
> -	{HID_USAGE_SENSOR_COMPASS_3D, 0, 0, 1000},
> +	{HID_USAGE_SENSOR_COMPASS_3D, 0, 0, 1000000},
>  	{HID_USAGE_SENSOR_COMPASS_3D, HID_USAGE_SENSOR_UNITS_GAUSS, 1, 0},
>  
> -	{HID_USAGE_SENSOR_INCLINOMETER_3D, 0, 0, 17453},
> +	{HID_USAGE_SENSOR_INCLINOMETER_3D, 0, 0, 17453293},
>  	{HID_USAGE_SENSOR_INCLINOMETER_3D,
> -		HID_USAGE_SENSOR_UNITS_DEGREES, 0, 17453},
> +		HID_USAGE_SENSOR_UNITS_DEGREES, 0, 17453293},
>  	{HID_USAGE_SENSOR_INCLINOMETER_3D,
>  		HID_USAGE_SENSOR_UNITS_RADIANS, 1, 0},
>  
> @@ -57,7 +57,7 @@
>  	{HID_USAGE_SENSOR_ALS, HID_USAGE_SENSOR_UNITS_LUX, 1, 0},
>  
>  	{HID_USAGE_SENSOR_PRESSURE, 0, 100, 0},
> -	{HID_USAGE_SENSOR_PRESSURE, HID_USAGE_SENSOR_UNITS_PASCAL, 0, 1000},
> +	{HID_USAGE_SENSOR_PRESSURE, HID_USAGE_SENSOR_UNITS_PASCAL, 0, 1000000},
>  };
>  
>  static int pow_10(unsigned power)
> @@ -266,15 +266,15 @@ int hid_sensor_write_raw_hyst_value(struct hid_sensor_common *st,
>  /*
>   * This fuction applies the unit exponent to the scale.
>   * For example:
> - * 9.806650 ->exp:2-> val0[980]val1[665000]
> - * 9.000806 ->exp:2-> val0[900]val1[80600]
> - * 0.174535 ->exp:2-> val0[17]val1[453500]
> - * 1.001745 ->exp:0-> val0[1]val1[1745]
> - * 1.001745 ->exp:2-> val0[100]val1[174500]
> - * 1.001745 ->exp:4-> val0[10017]val1[450000]
> - * 9.806650 ->exp:-2-> val0[0]val1[98066]
> + * 9.806650000 ->exp:2-> val0[980]val1[665000000]
> + * 9.000806000 ->exp:2-> val0[900]val1[80600000]
> + * 0.174535293 ->exp:2-> val0[17]val1[453529300]
> + * 1.001745329 ->exp:0-> val0[1]val1[1745329]
> + * 1.001745329 ->exp:2-> val0[100]val1[174532900]
> + * 1.001745329 ->exp:4-> val0[10017]val1[453290000]
> + * 9.806650000 ->exp:-2-> val0[0]val1[98066500]
>   */
> -static void adjust_exponent_micro(int *val0, int *val1, int scale0,
> +static void adjust_exponent_nano(int *val0, int *val1, int scale0,
>  				  int scale1, int exp)
>  {
>  	int i;
> @@ -285,32 +285,32 @@ static void adjust_exponent_micro(int *val0, int *val1, int scale0,
>  	if (exp > 0) {
>  		*val0 = scale0 * pow_10(exp);
>  		res = 0;
> -		if (exp > 6) {
> +		if (exp > 9) {
>  			*val1 = 0;
>  			return;
>  		}
>  		for (i = 0; i < exp; ++i) {
> -			x = scale1 / pow_10(5 - i);
> +			x = scale1 / pow_10(8 - i);
>  			res += (pow_10(exp - 1 - i) * x);
> -			scale1 = scale1 % pow_10(5 - i);
> +			scale1 = scale1 % pow_10(8 - i);
>  		}
>  		*val0 += res;
>  			*val1 = scale1 * pow_10(exp);
>  	} else if (exp < 0) {
>  		exp = abs(exp);
> -		if (exp > 6) {
> +		if (exp > 9) {
>  			*val0 = *val1 = 0;
>  			return;
>  		}
>  		*val0 = scale0 / pow_10(exp);
>  		rem = scale0 % pow_10(exp);
>  		res = 0;
> -		for (i = 0; i < (6 - exp); ++i) {
> -			x = scale1 / pow_10(5 - i);
> -			res += (pow_10(5 - exp - i) * x);
> -			scale1 = scale1 % pow_10(5 - i);
> +		for (i = 0; i < (9 - exp); ++i) {
> +			x = scale1 / pow_10(8 - i);
> +			res += (pow_10(8 - exp - i) * x);
> +			scale1 = scale1 % pow_10(8 - i);
>  		}
> -		*val1 = rem * pow_10(6 - exp) + res;
> +		*val1 = rem * pow_10(9 - exp) + res;
>  	} else {
>  		*val0 = scale0;
>  		*val1 = scale1;
> @@ -332,14 +332,14 @@ int hid_sensor_format_scale(u32 usage_id,
>  			unit_conversion[i].unit == attr_info->units) {
>  			exp  = hid_sensor_convert_exponent(
>  						attr_info->unit_expo);
> -			adjust_exponent_micro(val0, val1,
> +			adjust_exponent_nano(val0, val1,
>  					unit_conversion[i].scale_val0,
>  					unit_conversion[i].scale_val1, exp);
>  			break;
>  		}
>  	}
>  
> -	return IIO_VAL_INT_PLUS_MICRO;
> +	return IIO_VAL_INT_PLUS_NANO;
>  }
>  EXPORT_SYMBOL(hid_sensor_format_scale);
>  
>