[PATCH v5 6/7] iio: adc: stm32-adc: add vrefint calibration support

Olivier Moysan
2021-10-14T13:18:21Z

Add support of vrefint calibration.
If a channel is labeled as vrefint, get vrefint calibration
from non volatile memory for this channel.
vrefint channel is exposed as a processed channel returning
the actual value of vrefp:
vrefp = 3.3 x vrefint_cal / vrefint_data

A conversion on vrefint channel allows to update scale
factor according to vrefint deviation, compared to vrefint
calibration value.

Signed-off-by: Olivier Moysan <olivier.moysan@foss.st.com>
Reviewed-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
---
drivers/iio/adc/stm32-adc.c | 74 ++++++++++++++++++++++++++++++++++---
1 file changed, 68 insertions(+), 6 deletions(-)

diff --git a/drivers/iio/adc/stm32-adc.c b/drivers/iio/adc/stm32-adc.c
index 943ca03f4d31..5269bb87d094 100644
--- a/drivers/iio/adc/stm32-adc.c
+++ b/drivers/iio/adc/stm32-adc.c
@@ -21,6 +21,7 @@
#include <linux/io.h>
#include <linux/iopoll.h>
#include <linux/module.h>
+#include <linux/nvmem-consumer.h>
#include <linux/platform_device.h>
#include <linux/pm_runtime.h>
#include <linux/of.h>
@@ -41,6 +42,7 @@
#define STM32_ADC_TIMEOUT_US 100000
#define STM32_ADC_TIMEOUT (msecs_to_jiffies(STM32_ADC_TIMEOUT_US / 1000))
#define STM32_ADC_HW_STOP_DELAY_MS 100
+#define STM32_ADC_VREFINT_VOLTAGE 3300

#define STM32_DMA_BUFFER_SIZE PAGE_SIZE

@@ -137,6 +139,16 @@ struct stm32_adc_regs {
int shift;
};

+/**
+ * struct stm32_adc_vrefint - stm32 ADC internal reference voltage data
+ * @vrefint_cal: vrefint calibration value from nvmem
+ * @vrefint_data: vrefint actual value
+ */
+struct stm32_adc_vrefint {
+ u32 vrefint_cal;
+ u32 vrefint_data;
+};
+
/**
* struct stm32_adc_regspec - stm32 registers definition
* @dr: data register offset
@@ -186,6 +198,7 @@ struct stm32_adc;
* @unprepare: optional unprepare routine (disable, power-down)
* @irq_clear: routine to clear irqs
* @smp_cycles: programmable sampling time (ADC clock cycles)
+ * @ts_vrefint_ns: vrefint minimum sampling time in ns
*/
struct stm32_adc_cfg {
const struct stm32_adc_regspec *regs;
@@ -199,6 +212,7 @@ struct stm32_adc_cfg {
void (*unprepare)(struct iio_dev *);
void (*irq_clear)(struct iio_dev *indio_dev, u32 msk);
const unsigned int *smp_cycles;
+ const unsigned int ts_vrefint_ns;
};

/**
@@ -223,6 +237,7 @@ struct stm32_adc_cfg {
* @pcsel: bitmask to preselect channels on some devices
* @smpr_val: sampling time settings (e.g. smpr1 / smpr2)
* @cal: optional calibration data on some devices
+ * @vrefint: internal reference voltage data
* @chan_name: channel name array
* @num_diff: number of differential channels
* @int_ch: internal channel indexes array
@@ -248,6 +263,7 @@ struct stm32_adc {
u32 pcsel;
u32 smpr_val[2];
struct stm32_adc_calib cal;
+ struct stm32_adc_vrefint vrefint;
char chan_name[STM32_ADC_CH_MAX][STM32_ADC_CH_SZ];
u32 num_diff;
int int_ch[STM32_ADC_INT_CH_NB];
@@ -1339,6 +1355,7 @@ static int stm32_adc_read_raw(struct iio_dev *indio_dev,

switch (mask) {
case IIO_CHAN_INFO_RAW:
+ case IIO_CHAN_INFO_PROCESSED:
ret = iio_device_claim_direct_mode(indio_dev);
if (ret)
return ret;
@@ -1346,6 +1363,10 @@ static int stm32_adc_read_raw(struct iio_dev *indio_dev,
ret = stm32_adc_single_conv(indio_dev, chan, val);
else
ret = -EINVAL;
+
+ if (mask == IIO_CHAN_INFO_PROCESSED && adc->vrefint.vrefint_cal)
+ *val = STM32_ADC_VREFINT_VOLTAGE * adc->vrefint.vrefint_cal / *val;
+
iio_device_release_direct_mode(indio_dev);
return ret;

@@ -1815,7 +1836,10 @@ static void stm32_adc_chan_init_one(struct iio_dev *indio_dev,
chan->datasheet_name = name;
chan->scan_index = scan_index;
chan->indexed = 1;
- chan->info_mask_separate = BIT(IIO_CHAN_INFO_RAW);
+ if (chan->channel == adc->int_ch[STM32_ADC_INT_CH_VREFINT])
+ chan->info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED);
+ else
+ chan->info_mask_separate = BIT(IIO_CHAN_INFO_RAW);
chan->info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) |
BIT(IIO_CHAN_INFO_OFFSET);
chan->scan_type.sign = 'u';
@@ -1917,6 +1941,36 @@ static int stm32_adc_legacy_chan_init(struct iio_dev *indio_dev,
return scan_index;
}

+static int stm32_adc_populate_int_ch(struct iio_dev *indio_dev, const char *ch_name,
+ int chan)
+{
+ struct stm32_adc *adc = iio_priv(indio_dev);
+ u16 vrefint;
+ int i, ret;
+
+ for (i = 0; i < STM32_ADC_INT_CH_NB; i++) {
+ if (!strncmp(stm32_adc_ic[i].name, ch_name, STM32_ADC_CH_SZ)) {
+ adc->int_ch[i] = chan;
+
+ if (stm32_adc_ic[i].idx != STM32_ADC_INT_CH_VREFINT)
+ continue;
+
+ /* Get calibration data for vrefint channel */
+ ret = nvmem_cell_read_u16(&indio_dev->dev, "vrefint", &vrefint);
+ if (ret && ret != -ENOENT) {
+ return dev_err_probe(&indio_dev->dev, ret,
+ "nvmem access error\n");
+ }
+ if (ret == -ENOENT)
+ dev_dbg(&indio_dev->dev, "vrefint calibration not found\n");
+ else
+ adc->vrefint.vrefint_cal = vrefint;
+ }
+ }
+
+ return 0;
+}
+
static int stm32_adc_generic_chan_init(struct iio_dev *indio_dev,
struct stm32_adc *adc,
struct iio_chan_spec *channels)
@@ -1925,7 +1979,7 @@ static int stm32_adc_generic_chan_init(struct iio_dev *indio_dev,
const struct stm32_adc_info *adc_info = adc->cfg->adc_info;
struct device_node *child;
const char *name;
- int val, scan_index = 0, ret, i;
+ int val, scan_index = 0, ret;
bool differential;
u32 vin[2];

@@ -1945,10 +1999,9 @@ static int stm32_adc_generic_chan_init(struct iio_dev *indio_dev,
return -EINVAL;
}
strncpy(adc->chan_name[val], name, STM32_ADC_CH_SZ);
- for (i = 0; i < STM32_ADC_INT_CH_NB; i++) {
- if (!strncmp(stm32_adc_ic[i].name, name, STM32_ADC_CH_SZ))
- adc->int_ch[i] = val;
- }
+ ret = stm32_adc_populate_int_ch(indio_dev, name, val);
+ if (ret)
+ goto err;
} else if (ret != -EINVAL) {
dev_err(&indio_dev->dev, "Invalid label %d\n", ret);
goto err;
@@ -2055,6 +2108,14 @@ static int stm32_adc_chan_of_init(struct iio_dev *indio_dev, bool timestamping)
*/
of_property_read_u32_index(node, "st,min-sample-time-nsecs",
i, &smp);
+
+ /*
+ * For vrefint channel, ensure that the sampling time cannot
+ * be lower than the one specified in the datasheet
+ */
+ if (channels[i].channel == adc->int_ch[STM32_ADC_INT_CH_VREFINT])
+ smp = max(smp, adc->cfg->ts_vrefint_ns);
+
/* Prepare sampling time settings */
stm32_adc_smpr_init(adc, channels[i].channel, smp);
}
@@ -2361,6 +2422,7 @@ static const struct stm32_adc_cfg stm32mp1_adc_cfg = {
.unprepare = stm32h7_adc_unprepare,
.smp_cycles = stm32h7_adc_smp_cycles,
.irq_clear = stm32h7_adc_irq_clear,
+ .ts_vrefint_ns = 4300,
};

static const struct of_device_id stm32_adc_of_match[] = {