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SubjectRe: [PATCH v2 3/3] iio: dps310: Add pressure sensing capability
On Tue, 14 May 2019 15:25:55 -0500
Eddie James <eajames@linux.vnet.ibm.com> wrote:

> On 5/11/19 4:48 AM, Jonathan Cameron wrote:
> > On Wed, 8 May 2019 14:35:28 -0500
> > Eddie James <eajames@linux.ibm.com> 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@linux.ibm.com>
> > 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.
That would be a 'slightly' interesting interpretation of the ABI, but
I'd 'probably' let it go as any correct userspace should be fine
receiving data at a higher rate than it asked for.

Jonathan
>
> 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;
> >>
>

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