[PATCH v4 06/10] drivers: iio: imu: adis16475: generic computation for sample rate

[Ramona Gradinariu <ramona.bolboaca13@gmail.com>]

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.

Signed-off-by: Ramona Gradinariu <ramona.bolboaca13@gmail.com>
---
no changes in v4
 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 ab955efdad92..c589f214259b 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);
@@ -1359,6 +1364,7 @@ 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;
@@ -1398,10 +1404,9 @@ 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