iio: adc: stm32-adc: add vrefint calibration support

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>
Link: https://lore.kernel.org/r/20211014131228.4692-7-olivier.moysan@foss.st.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

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];
@@ -1339,13 +1355,18 @@ 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;
 		if (chan->type == IIO_VOLTAGE)
 			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[] = {