Re: [PATCH v2 3/3] iio: dps310: Add pressure sensing capability

[Eddie James <eajames@xxxxxxxxxxxxxxxxxx>]

On 5/11/19 4:48 AM, Jonathan Cameron wrote:
> On Wed,  8 May 2019 14:35:28 -0500
> Eddie James <eajames@xxxxxxxxxxxxx> wrote:
>
> > The DPS310 supports measurement of pressure, so support that in the
> > driver. Use background measurement like the temperature sensing and
> > default to lowest precision and lowest measurement rate.
> >
> > Signed-off-by: Eddie James <eajames@xxxxxxxxxxxxx>
> Hi Eddie,
>
> A few comments inline.  One is around how you might look at adding
> fifo support (pushing to an IIO buffer) in the future...  The IIO
> data model isn't as flexible as this device can be, so we may need
> to put some restrictions on combinations of options.
>
> Jonathan
> > ---
> >   drivers/iio/pressure/dps310.c | 331 +++++++++++++++++++++++++++++++++++++++---
> >   1 file changed, 307 insertions(+), 24 deletions(-)
> >
> > diff --git a/drivers/iio/pressure/dps310.c b/drivers/iio/pressure/dps310.c
> > index c42808e..a7ee28c 100644
> > --- a/drivers/iio/pressure/dps310.c
> > +++ b/drivers/iio/pressure/dps310.c
> > @@ -11,11 +11,11 @@
> >    *   c0 * 0.5 + c1 * T_raw / kT °C
> >    *
> >    * TODO:
> > - *  - Pressure sensor readings
> >    *  - Optionally support the FIFO
> >    */
> >   
> >   #include <linux/i2c.h>
> > +#include <linux/math64.h>
> >   #include <linux/module.h>
> >   #include <linux/regmap.h>
> >   
> > @@ -29,6 +29,8 @@
> >   #define DPS310_TMP_B1		0x04
> >   #define DPS310_TMP_B2		0x05
> >   #define DPS310_PRS_CFG		0x06
> > +#define  DPS310_PRS_RATE_BITS	GENMASK(6, 4)
> > +#define  DPS310_PRS_PRC_BITS	GENMASK(3, 0)
> >   #define DPS310_TMP_CFG		0x07
> >   #define  DPS310_TMP_RATE_BITS	GENMASK(6, 4)
> >   #define  DPS310_TMP_PRC_BITS	GENMASK(3, 0)
> > @@ -82,6 +84,8 @@ struct dps310_data {
> >   	struct regmap *regmap;
> >   

> > +
> >   static bool dps310_is_writeable_reg(struct device *dev, unsigned int reg)
> >   {
> >   	switch (reg) {
> > @@ -253,24 +387,141 @@ static int dps310_write_raw(struct iio_dev *iio,
> >   {
> >   	struct dps310_data *data = iio_priv(iio);
> >   
> > -	if (chan->type != IIO_TEMP)
> > +	switch (mask) {
> > +	case IIO_CHAN_INFO_SAMP_FREQ:
> > +		switch (chan->type) {
> > +		case IIO_PRESSURE:
> > +			return dps310_set_pres_samp_freq(data, val);
> > +
> > +		case IIO_TEMP:
> > +			return dps310_set_temp_samp_freq(data, val);
> This may need a bit of thought if there is any chance we will later support
> the fifo.
>
> The IIO model is that of scans that read all channels at each 'trigger'. In
> devices like this which allow for different sampling rates for different sensor
> channels there are two options.
>
> 1) Don't support it.
> 2) Deal with registering two separate IIO devices and do the demux in the
> driver to the relevant one.
>
> All depends on whether there is a substantial usecase for different sampling
> rates or not.  Here I suspect the answer is not.
>
> The complexity is that, you then need to work out how to 'upgrade' the
> interface when buffered support is added. Obvious options are:
>
> 1) Refuse to move to buffered mode if the sampling frequencies are different.
> 2) Force the slower channel to be sampled faster if that is possible.
> 3) Change to only having one exposed sampling frequency at all - the problem
> with this last one is that it changes the ABI for existing users.
>
> It may be no one ever cares about the fifo mode though as high speed pressure
> measurement is 'unusual' ;)


Thanks for the comments Jonathan. I will follow your suggestions 
throughout the driver.

The sampling rates are a bit confusing for me, and I haven't looked into 
the buffered mode at all. Are you saying that in the current form, it 
won't work to use different sampling frequencies for the two sensors 
(without buffered mode I mean)? I haven't noticed any problems in my 
tests. I'm inclined force the slower channel to be sampled faster if 
necessary when buffered mode is implemented.

Thanks,

Eddie


> > +
> > +		default:
> > +			return -EINVAL;
> > +		}
> > +
> > +	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
> > +		switch (chan->type) {
> > +		case IIO_PRESSURE:
> > +			return dps310_set_pres_precision(data, val);
> > +
> > +		case IIO_TEMP:
> > +			return dps310_set_temp_precision(data, val);
> > +
> > +		default:
> > +			return -EINVAL;
> > +		}
> > +
> > +	default:
> >   		return -EINVAL;
> > +	}
> > +}
> > +
> > +static int dps310_calculate_pressure(struct dps310_data *data)
> > +{
> > +	int i, r, t_ready;
> > +	int kpi = dps310_get_pres_k(data);
> > +	int kti = dps310_get_temp_k(data);
> > +	s64 rem = 0ULL;
> > +	s64 pressure = 0ULL;
> > +	s64 p;
> > +	s64 t;
> > +	s64 denoms[7];
> > +	s64 nums[7];
> > +	s64 rems[7];
> > +	s64 kp;
> > +	s64 kt;
> > +
> > +	if (kpi < 0)
> > +		return kpi;
> > +
> > +	if (kti < 0)
> > +		return kti;
> > +
> > +	kp = (s64)kpi;
> > +	kt = (s64)kti;
> > +
> > +	/* Refresh temp if it's ready, otherwise just use the latest value */
> > +	r = regmap_read(data->regmap, DPS310_MEAS_CFG, &t_ready);
> > +	if (r >= 0 && t_ready & DPS310_TMP_RDY)
> > +		dps310_read_temp_ready(data);
> > +
> > +	p = (s64)data->pressure_raw;
> > +	t = (s64)data->temp_raw;
> > +
> > +	/* Section 4.9.1 of the DPS310 spec; algebra'd to avoid underflow */
> > +	nums[0] = (s64)data->c00;
> > +	denoms[0] = 1LL;
> > +	nums[1] = p * (s64)data->c10;
> > +	denoms[1] = kp;
> > +	nums[2] = p * p * (s64)data->c20;
> > +	denoms[2] = kp * kp;
> > +	nums[3] = p * p * p * (s64)data->c30;
> > +	denoms[3] = kp * kp * kp;
> > +	nums[4] = t * (s64)data->c01;
> > +	denoms[4] = kt;
> > +	nums[5] = t * p * (s64)data->c11;
> > +	denoms[5] = kp * kt;
> > +	nums[6] = t * p * p * (s64)data->c21;
> > +	denoms[6] = kp * kp * kt;
> > +
> > +	/* Kernel lacks a div64_s64_rem function; denoms are all positive */
> > +	for (i = 0; i < 7; ++i) {
> > +		u64 rem;
> > +
> > +		if (nums[i] < 0LL) {
> > +			pressure -= div64_u64_rem(-nums[i], denoms[i], &rem);
> > +			rems[i] = -rem;
> > +		} else {
> > +			pressure += div64_u64_rem(nums[i], denoms[i], &rem);
> > +			rems[i] = (s64)rem;
> > +		}
> > +	}
> > +
> > +	/* Increase precision and calculate the remainder sum */
> > +	for (i = 0; i < 7; ++i)
> > +		rem += div64_s64((s64)rems[i] * 1000000000LL, denoms[i]);
> > +
> > +	pressure += div_s64(rem, 1000000000LL);
> > +
> > +	return (int)pressure;
> > +}
> > +
> > +static int dps310_read_pressure(struct dps310_data *data, int *val, int *val2,
> > +				long mask)
> > +{
> > +	int ret;
> >   
> >   	switch (mask) {
> >   	case IIO_CHAN_INFO_SAMP_FREQ:
> > -		return dps310_set_temp_samp_freq(data, val);
> > +		*val = dps310_get_pres_samp_freq(data);
> > +		return IIO_VAL_INT;
> > +
> > +	case IIO_CHAN_INFO_RAW:
> > +		ret = dps310_read_pres_raw(data);
> > +		if (ret)
> > +			return ret;
> > +
> > +		*val = dps310_calculate_pressure(data);
> This is rather far from raw :)  It might be better at this point to just
> go for PROCESSED and apply the scale in here.
>
> > +		return IIO_VAL_INT;
> > +
> > +	case IIO_CHAN_INFO_SCALE:
> > +		*val = 1;
> > +		*val2 = 1000; /* Convert Pa to KPa per IIO ABI */
> > +		return IIO_VAL_FRACTIONAL;
> > +
> >   	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
> > -		return dps310_set_temp_precision(data, val);
> > +		*val = dps310_get_pres_precision(data);
> > +		return IIO_VAL_INT;
> > +
> >   	default:
> >   		return -EINVAL;
> >   	}
> >   }
> >   
> > -static int dps310_read_raw(struct iio_dev *iio,
> > -			   struct iio_chan_spec const *chan,
> > -			   int *val, int *val2, long mask)
> > +static int dps310_read_temp(struct dps310_data *data, int *val, int *val2,
> > +			    long mask)
> >   {
> > -	struct dps310_data *data = iio_priv(iio);
> >   	int ret;
> >   
> >   	switch (mask) {
> > @@ -279,7 +530,7 @@ static int dps310_read_raw(struct iio_dev *iio,
> >   		return IIO_VAL_INT;
> >   
> >   	case IIO_CHAN_INFO_RAW:
> > -		ret = dps310_read_temp(data);
> > +		ret = dps310_read_temp_raw(data);
> >   		if (ret)
> >   			return ret;
> >   
> > @@ -312,6 +563,24 @@ static int dps310_read_raw(struct iio_dev *iio,
> >   	}
> >   }
> >   
> > +static int dps310_read_raw(struct iio_dev *iio,
> > +			   struct iio_chan_spec const *chan,
> > +			   int *val, int *val2, long mask)
> > +{
> > +	struct dps310_data *data = iio_priv(iio);
> > +
> > +	switch (chan->type) {
> > +	case IIO_PRESSURE:
> > +		return dps310_read_pressure(data, val, val2, mask);
> > +
> > +	case IIO_TEMP:
> > +		return dps310_read_temp(data, val, val2, mask);
> > +
> > +	default:
> > +		return -EINVAL;
> > +	}
> > +}
> > +
> >   static const struct regmap_config dps310_regmap_config = {
> >   	.reg_bits = 8,
> >   	.val_bits = 8,
> > @@ -393,6 +662,13 @@ static int dps310_probe(struct i2c_client *client,
> >   		return PTR_ERR(data->regmap);
> >   
> >   	/*
> > +	 * Set up pressure sensor in single sample, one measurement per second
> > +	 * mode
> > +	 */
> > +	r = regmap_write(data->regmap, DPS310_PRS_CFG,
> > +			 DPS310_CALC_RATE(1) | DPS310_CALC_PRC(1));
> > +
> > +	/*
> >   	 * Set up external (MEMS) temperature sensor in single sample, one
> >   	 * measurement per second mode
> >   	 */
> > @@ -402,16 +678,23 @@ static int dps310_probe(struct i2c_client *client,
> >   	if (r < 0)
> >   		goto err;
> >   
> > -	/* Temp shift is disabled when PRC <= 8 */
> > +	/* Temp and pressure shifts are disabled when PRC <= 8 */
> >   	r = regmap_write_bits(data->regmap, DPS310_CFG_REG,
> > -			      DPS310_TMP_SHIFT_EN, 0);
> > +			      DPS310_TMP_SHIFT_EN | DPS310_PRS_SHIFT_EN, 0);
> > +	if (r < 0)
> > +		goto err;
> > +
> > +	/* MEAS_CFG doesn't seem to update unless first written with 0 */
> > +	r = regmap_write_bits(data->regmap, DPS310_MEAS_CFG,
> > +			      DPS310_MEAS_CTRL_BITS, 0);
> >   	if (r < 0)
> >   		goto err;
> >   
> > -	/* Turn on temperature measurement in the background */
> > +	/* Turn on temperature and pressure measurement in the background */
> >   	r = regmap_write_bits(data->regmap, DPS310_MEAS_CFG,
> >   			      DPS310_MEAS_CTRL_BITS,
> > -			      DPS310_TEMP_EN | DPS310_BACKGROUND);
> > +			      DPS310_PRS_EN | DPS310_TEMP_EN |
> > +			      DPS310_BACKGROUND);
> >   	if (r < 0)
> >   		goto err;
> >   
> > @@ -424,7 +707,7 @@ static int dps310_probe(struct i2c_client *client,
> >   	if (r < 0)
> >   		goto err;
> >   
> > -	r = dps310_get_temp_coef(data);
> > +	r = dps310_get_coefs(data);
> >   	if (r < 0)
> >   		goto err;
> >