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

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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