[PATCH v5 5/9] drivers: iio: imu: adis16475: generic computation for sample rate

Ramona Gradinariu
2024-05-27T14:26:31Z

Currently adis16475 supports a sample rate between 1900 and 2100 Hz.
This patch changes the setting of sample rate from hardcoded values to
a generic computation based on the internal clock frequency.
This is a preparatory patch for adding support for adis1657x family
devices which allow sample rates between 3900 and 4100 Hz.

Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Signed-off-by: Ramona Gradinariu <ramona.bolboaca13@gmail.com>
---
no changes in v5
drivers/iio/imu/adis16475.c | 39 +++++++++++++++++++++----------------
1 file changed, 22 insertions(+), 17 deletions(-)

diff --git a/drivers/iio/imu/adis16475.c b/drivers/iio/imu/adis16475.c
index 64c8bdaba4c5..b1def85b6f90 100644
--- a/drivers/iio/imu/adis16475.c
+++ b/drivers/iio/imu/adis16475.c
@@ -310,6 +310,9 @@ static int adis16475_set_freq(struct adis16475 *st, const u32 freq)
u16 dec;
int ret;
u32 sample_rate = st->clk_freq;
+ /* The optimal sample rate for the supported IMUs is between int_clk - 100 and int_clk + 100. */
+ u32 max_sample_rate = st->info->int_clk * 1000 + 100000;
+ u32 min_sample_rate = st->info->int_clk * 1000 - 100000;

if (!freq)
return -EINVAL;
@@ -317,8 +320,9 @@ static int adis16475_set_freq(struct adis16475 *st, const u32 freq)
adis_dev_lock(&st->adis);
/*
* When using sync scaled mode, the input clock needs to be scaled so that we have
- * an IMU sample rate between (optimally) 1900 and 2100. After this, we can use the
- * decimation filter to lower the sampling rate in order to get what the user wants.
+ * an IMU sample rate between (optimally) int_clk - 100 and int_clk + 100.
+ * After this, we can use the decimation filter to lower the sampling rate in order
+ * to get what the user wants.
* Optimally, the user sample rate is a multiple of both the IMU sample rate and
* the input clock. Hence, calculating the sync_scale dynamically gives us better
* chances of achieving a perfect/integer value for DEC_RATE. The math here is:
@@ -336,23 +340,24 @@ static int adis16475_set_freq(struct adis16475 *st, const u32 freq)
* solution. In this case, we get the highest multiple of the input clock
* lower than the IMU max sample rate.
*/
- if (scaled_rate > 2100000)
- scaled_rate = 2100000 / st->clk_freq * st->clk_freq;
+ if (scaled_rate > max_sample_rate)
+ scaled_rate = max_sample_rate / st->clk_freq * st->clk_freq;
else
- scaled_rate = 2100000 / scaled_rate * scaled_rate;
+ scaled_rate = max_sample_rate / scaled_rate * scaled_rate;

/*
* This is not an hard requirement but it's not advised to run the IMU
- * with a sample rate lower than 1900Hz due to possible undersampling
- * issues. However, there are users that might really want to take the risk.
- * Hence, we provide a module parameter for them. If set, we allow sample
- * rates lower than 1.9KHz. By default, we won't allow this and we just roundup
- * the rate to the next multiple of the input clock bigger than 1.9KHz. This
- * is done like this as in some cases (when DEC_RATE is 0) might give
- * us the closest value to the one desired by the user...
+ * with a sample rate lower than internal clock frequency, due to possible
+ * undersampling issues. However, there are users that might really want
+ * to take the risk. Hence, we provide a module parameter for them. If set,
+ * we allow sample rates lower than internal clock frequency.
+ * By default, we won't allow this and we just roundup the rate to the next
+ * multiple of the input clock. This is done like this as in some cases
+ * (when DEC_RATE is 0) might give us the closest value to the one desired
+ * by the user...
*/
- if (scaled_rate < 1900000 && !low_rate_allow)
- scaled_rate = roundup(1900000, st->clk_freq);
+ if (scaled_rate < min_sample_rate && !low_rate_allow)
+ scaled_rate = roundup(min_sample_rate, st->clk_freq);

sync_scale = scaled_rate / st->clk_freq;
ret = __adis_write_reg_16(&st->adis, ADIS16475_REG_UP_SCALE, sync_scale);
@@ -1317,6 +1322,7 @@ static int adis16475_config_sync_mode(struct adis16475 *st)
struct device *dev = &st->adis.spi->dev;
const struct adis16475_sync *sync;
u32 sync_mode;
+ u16 max_sample_rate = st->info->int_clk + 100;

/* default to internal clk */
st->clk_freq = st->info->int_clk * 1000;
@@ -1356,10 +1362,9 @@ static int adis16475_config_sync_mode(struct adis16475 *st)
/*
* In sync scaled mode, the IMU sample rate is the clk_freq * sync_scale.
* Hence, default the IMU sample rate to the highest multiple of the input
- * clock lower than the IMU max sample rate. The optimal range is
- * 1900-2100 sps...
+ * clock lower than the IMU max sample rate.
*/
- up_scale = 2100 / st->clk_freq;
+ up_scale = max_sample_rate / st->clk_freq;

ret = __adis_write_reg_16(&st->adis,
ADIS16475_REG_UP_SCALE,
--
2.34.1