diff options
Diffstat (limited to 'drivers/iio/imu')
| -rw-r--r-- | drivers/iio/imu/adis16480.c | 128 |
1 files changed, 94 insertions, 34 deletions
diff --git a/drivers/iio/imu/adis16480.c b/drivers/iio/imu/adis16480.c index dfe86c589325..c41b8ef1e250 100644 --- a/drivers/iio/imu/adis16480.c +++ b/drivers/iio/imu/adis16480.c @@ -10,6 +10,7 @@ #include <linux/of_irq.h> #include <linux/interrupt.h> #include <linux/delay.h> +#include <linux/math.h> #include <linux/mutex.h> #include <linux/device.h> #include <linux/kernel.h> @@ -17,6 +18,7 @@ #include <linux/slab.h> #include <linux/sysfs.h> #include <linux/module.h> +#include <linux/lcm.h> #include <linux/iio/iio.h> #include <linux/iio/sysfs.h> @@ -170,6 +172,11 @@ static const char * const adis16480_int_pin_names[4] = { [ADIS16480_PIN_DIO4] = "DIO4", }; +static bool low_rate_allow; +module_param(low_rate_allow, bool, 0444); +MODULE_PARM_DESC(low_rate_allow, + "Allow IMU rates below the minimum advisable when external clk is used in PPS mode (default: N)"); + #ifdef CONFIG_DEBUG_FS static ssize_t adis16480_show_firmware_revision(struct file *file, @@ -312,7 +319,8 @@ static int adis16480_debugfs_init(struct iio_dev *indio_dev) static int adis16480_set_freq(struct iio_dev *indio_dev, int val, int val2) { struct adis16480 *st = iio_priv(indio_dev); - unsigned int t, reg; + unsigned int t, sample_rate = st->clk_freq; + int ret; if (val < 0 || val2 < 0) return -EINVAL; @@ -321,28 +329,65 @@ static int adis16480_set_freq(struct iio_dev *indio_dev, int val, int val2) if (t == 0) return -EINVAL; + mutex_lock(&st->adis.state_lock); /* - * When using PPS mode, the rate of data collection is equal to the - * product of the external clock frequency and the scale factor in the - * SYNC_SCALE register. - * When using sync mode, or internal clock, the output data rate is - * equal with the clock frequency divided by DEC_RATE + 1. + * When using PPS mode, the input clock needs to be scaled so that we have an IMU + * sample rate between (optimally) 4000 and 4250. 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: + * 1. lcm of the input clock and the desired output rate. + * 2. get the highest multiple of the previous result lower than the adis max rate. + * 3. The last result becomes the IMU sample rate. Use that to calculate SYNC_SCALE + * and DEC_RATE (to get the user output rate) */ if (st->clk_mode == ADIS16480_CLK_PPS) { - t = t / st->clk_freq; - reg = ADIS16495_REG_SYNC_SCALE; - } else { - t = st->clk_freq / t; - reg = ADIS16480_REG_DEC_RATE; + unsigned long scaled_rate = lcm(st->clk_freq, t); + int sync_scale; + + /* + * If lcm is bigger than the IMU maximum sampling rate there's no perfect + * solution. In this case, we get the highest multiple of the input clock + * lower than the IMU max sample rate. + */ + if (scaled_rate > st->chip_info->int_clk) + scaled_rate = st->chip_info->int_clk / st->clk_freq * st->clk_freq; + else + scaled_rate = st->chip_info->int_clk / 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 4000Hz 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 4KHz. By default, we won't allow this and we just roundup + * the rate to the next multiple of the input clock bigger than 4KHz. 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 < 4000000 && !low_rate_allow) + scaled_rate = roundup(4000000, st->clk_freq); + + sync_scale = scaled_rate / st->clk_freq; + ret = __adis_write_reg_16(&st->adis, ADIS16495_REG_SYNC_SCALE, sync_scale); + if (ret) + goto error; + + sample_rate = scaled_rate; } + t = DIV_ROUND_CLOSEST(sample_rate, t); + if (t) + t--; + if (t > st->chip_info->max_dec_rate) t = st->chip_info->max_dec_rate; - if ((t != 0) && (st->clk_mode != ADIS16480_CLK_PPS)) - t--; - - return adis_write_reg_16(&st->adis, reg, t); + ret = __adis_write_reg_16(&st->adis, ADIS16480_REG_DEC_RATE, t); +error: + mutex_unlock(&st->adis.state_lock); + return ret; } static int adis16480_get_freq(struct iio_dev *indio_dev, int *val, int *val2) @@ -350,34 +395,35 @@ static int adis16480_get_freq(struct iio_dev *indio_dev, int *val, int *val2) struct adis16480 *st = iio_priv(indio_dev); uint16_t t; int ret; - unsigned int freq; - unsigned int reg; + unsigned int freq, sample_rate = st->clk_freq; - if (st->clk_mode == ADIS16480_CLK_PPS) - reg = ADIS16495_REG_SYNC_SCALE; - else - reg = ADIS16480_REG_DEC_RATE; + mutex_lock(&st->adis.state_lock); + + if (st->clk_mode == ADIS16480_CLK_PPS) { + u16 sync_scale; + + ret = __adis_read_reg_16(&st->adis, ADIS16495_REG_SYNC_SCALE, &sync_scale); + if (ret) + goto error; - ret = adis_read_reg_16(&st->adis, reg, &t); + sample_rate = st->clk_freq * sync_scale; + } + + ret = __adis_read_reg_16(&st->adis, ADIS16480_REG_DEC_RATE, &t); if (ret) - return ret; + goto error; - /* - * When using PPS mode, the rate of data collection is equal to the - * product of the external clock frequency and the scale factor in the - * SYNC_SCALE register. - * When using sync mode, or internal clock, the output data rate is - * equal with the clock frequency divided by DEC_RATE + 1. - */ - if (st->clk_mode == ADIS16480_CLK_PPS) - freq = st->clk_freq * t; - else - freq = st->clk_freq / (t + 1); + mutex_unlock(&st->adis.state_lock); + + freq = DIV_ROUND_CLOSEST(sample_rate, (t + 1)); *val = freq / 1000; *val2 = (freq % 1000) * 1000; return IIO_VAL_INT_PLUS_MICRO; +error: + mutex_unlock(&st->adis.state_lock); + return ret; } enum { @@ -1278,6 +1324,20 @@ static int adis16480_probe(struct spi_device *spi) st->clk_freq = clk_get_rate(st->ext_clk); st->clk_freq *= 1000; /* micro */ + if (st->clk_mode == ADIS16480_CLK_PPS) { + u16 sync_scale; + + /* + * In PPS 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 internal sample rate is the + * max... + */ + sync_scale = st->chip_info->int_clk / st->clk_freq; + ret = __adis_write_reg_16(&st->adis, ADIS16495_REG_SYNC_SCALE, sync_scale); + if (ret) + return ret; + } } else { st->clk_freq = st->chip_info->int_clk; } |