iio: adc: stm32: add oversampling support

Add oversampling support for STM32H7, STM32MP15 & STM32MP13.
STM32F4 ADC has no oversampling feature.

The current support of the oversampling feature aims at increasing the
data SNR, without changing the data resolution.
As the oversampling by itself increases data resolution, a right shift
is applied to keep the initial resolution.
Only the oversampling ratio corresponding to a power of two are
supported here, to get a direct link between right shift and
oversampling ratio. (2^n ratio <=> n right shift)

The oversampling ratio is shared by all channels, whatever channel type.
(e.g. single ended or differential).

Oversampling can be configured using IIO ABI:
- oversampling_ratio_available
- oversampling_ratio

Co-developed-by: Fabrice Gasnier <[e-mail]>
Signed-off-by: Fabrice Gasnier <[e-mail]>
Signed-off-by: Olivier Moysan <[e-mail]>
Reviewed-by: David Lechner <[e-mail]>
Reviewed-by: Andy Shevchenko <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/adc/stm32-adc-core.h

···
 #ifndef __STM32_ADC_H
 #define __STM32_ADC_H
 
+#include <linux/bitfield.h>
+#include <linux/bits.h>
+
 /*
  * STM32 - ADC global register map
  * ________________________________________________________
···
 #define STM32H7_ADC_IER			0x04
 #define STM32H7_ADC_CR			0x08
 #define STM32H7_ADC_CFGR		0x0C
+#define STM32H7_ADC_CFGR2		0x10
 #define STM32H7_ADC_SMPR1		0x14
 #define STM32H7_ADC_SMPR2		0x18
 #define STM32H7_ADC_PCSEL		0x1C
···
 #define STM32H7_DMNGT_SHIFT		0
 #define STM32H7_DMNGT_MASK		GENMASK(1, 0)
 
+/* STM32H7_ADC_CFGR2 bit fields */
+#define STM32H7_OVSR_MASK		GENMASK(25, 16) /* Correspond to OSVR field in datasheet */
+#define STM32H7_OVSR(v)			FIELD_PREP(STM32H7_OVSR_MASK, v)
+#define STM32H7_OVSS_MASK		GENMASK(8, 5)
+#define STM32H7_OVSS(v)			FIELD_PREP(STM32H7_OVSS_MASK, v)
+#define STM32H7_ROVSE			BIT(0)
+
 enum stm32h7_adc_dmngt {
 	STM32H7_DMNGT_DR_ONLY,		/* Regular data in DR only */
 	STM32H7_DMNGT_DMA_ONESHOT,	/* DMA one shot mode */
···
 #define STM32MP13_DFSDMCFG		BIT(2)
 #define STM32MP13_RES_SHIFT		3
 #define STM32MP13_RES_MASK		GENMASK(4, 3)
+
+/* STM32MP13_ADC_CFGR2 bit fields */
+#define STM32MP13_OVSR_MASK		GENMASK(4, 2)
+#define STM32MP13_OVSR(v)		FIELD_PREP(STM32MP13_OVSR_MASK, v)
+#define STM32MP13_OVSS_MASK		GENMASK(8, 5)
+#define STM32MP13_OVSS(v)		FIELD_PREP(STM32MP13_OVSS_MASK, v)
 
 /* STM32MP13_ADC_DIFSEL - bit fields */
 #define STM32MP13_DIFSEL_MASK		GENMASK(18, 0)

drivers/iio/adc/stm32-adc.c

···
  * Author: Fabrice Gasnier <[e-mail]>.
  */
 
+#include <linux/array_size.h>
 #include <linux/clk.h>
 #include <linux/debugfs.h>
 #include <linux/delay.h>
···
  * @has_boostmode:	boost mode support flag
  * @has_linearcal:	linear calibration support flag
  * @has_presel:		channel preselection support flag
+ * @has_oversampling:	oversampling support flag
  * @prepare:		optional prepare routine (power-up, enable)
  * @start_conv:		routine to start conversions
  * @stop_conv:		routine to stop conversions
  * @unprepare:		optional unprepare routine (disable, power-down)
  * @irq_clear:		routine to clear irqs
+ * @set_ovs:		routine to set oversampling configuration
  * @smp_cycles:		programmable sampling time (ADC clock cycles)
  * @ts_int_ch:		pointer to array of internal channels minimum sampling time in ns
  */
···
 	bool has_boostmode;
 	bool has_linearcal;
 	bool has_presel;
+	bool has_oversampling;
 	int (*prepare)(struct iio_dev *);
 	void (*start_conv)(struct iio_dev *, bool dma);
 	void (*stop_conv)(struct iio_dev *);
 	void (*unprepare)(struct iio_dev *);
 	void (*irq_clear)(struct iio_dev *indio_dev, u32 msk);
+	void (*set_ovs)(struct iio_dev *indio_dev, u32 ovs_idx);
 	const unsigned int *smp_cycles;
 	const unsigned int *ts_int_ch;
 };
···
  * @num_diff:		number of differential channels
  * @int_ch:		internal channel indexes array
  * @nsmps:		number of channels with optional sample time
+ * @ovs_idx:		current oversampling ratio index (in oversampling array)
  */
 struct stm32_adc {
 	struct stm32_adc_common	*common;
···
 	u32			num_diff;
 	int			int_ch[STM32_ADC_INT_CH_NB];
 	int			nsmps;
+	int			ovs_idx;
 };
 
 struct stm32_adc_diff_channel {
···
  * struct stm32_adc_info - stm32 ADC, per instance config data
  * @max_channels:	Number of channels
  * @resolutions:	available resolutions
+ * @oversampling:	available oversampling ratios
  * @num_res:		number of available resolutions
+ * @num_ovs:		number of available oversampling ratios
  */
 struct stm32_adc_info {
 	int max_channels;
 	const unsigned int *resolutions;
+	const unsigned int *oversampling;
 	const unsigned int num_res;
+	const unsigned int num_ovs;
+};
+
+static const unsigned int stm32h7_adc_oversampling_avail[] = {
+	1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024,
+};
+
+static const unsigned int stm32mp13_adc_oversampling_avail[] = {
+	1, 2, 4, 8, 16, 32, 64, 128, 256,
 };
 
 static const unsigned int stm32f4_adc_resolutions[] = {
···
 static const struct stm32_adc_info stm32h7_adc_info = {
 	.max_channels = STM32_ADC_CH_MAX,
 	.resolutions = stm32h7_adc_resolutions,
+	.oversampling = stm32h7_adc_oversampling_avail,
 	.num_res = ARRAY_SIZE(stm32h7_adc_resolutions),
+	.num_ovs = ARRAY_SIZE(stm32h7_adc_oversampling_avail),
 };
 
 /* stm32mp13 can have up to 19 channels */
 static const struct stm32_adc_info stm32mp13_adc_info = {
 	.max_channels = 19,
 	.resolutions = stm32f4_adc_resolutions,
+	.oversampling = stm32mp13_adc_oversampling_avail,
 	.num_res = ARRAY_SIZE(stm32f4_adc_resolutions),
+	.num_ovs = ARRAY_SIZE(stm32mp13_adc_oversampling_avail),
 };
 
 /*
···
 				   STM32MP13_DMAEN | STM32MP13_DMACFG);
 
 	stm32_adc_set_bits(adc, STM32H7_ADC_CR, STM32H7_ADSTART);
+}
+
+static void stm32h7_adc_set_ovs(struct iio_dev *indio_dev, u32 ovs_idx)
+{
+	struct stm32_adc *adc = iio_priv(indio_dev);
+	u32 ovsr_bits, bits, msk;
+
+	msk = STM32H7_ROVSE | STM32H7_OVSR_MASK | STM32H7_OVSS_MASK;
+	stm32_adc_clr_bits(adc, STM32H7_ADC_CFGR2, msk);
+
+	if (!ovs_idx)
+		return;
+
+	/*
+	 * Only the oversampling ratios corresponding to 2^ovs_idx are exposed in sysfs.
+	 * Oversampling ratios [2,3,...,1024] are mapped on OVSR register values [1,2,...,1023].
+	 * OVSR = 2^ovs_idx - 1
+	 * These ratio increase the resolution by ovs_idx bits. Apply a right shift to keep initial
+	 * resolution given by "assigned-resolution-bits" property.
+	 * OVSS = ovs_idx
+	 */
+	ovsr_bits = GENMASK(ovs_idx - 1, 0);
+	bits = STM32H7_ROVSE | STM32H7_OVSS(ovs_idx) | STM32H7_OVSR(ovsr_bits);
+
+	stm32_adc_set_bits(adc, STM32H7_ADC_CFGR2, bits & msk);
+}
+
+static void stm32mp13_adc_set_ovs(struct iio_dev *indio_dev, u32 ovs_idx)
+{
+	struct stm32_adc *adc = iio_priv(indio_dev);
+	u32 bits, msk;
+
+	msk = STM32H7_ROVSE | STM32MP13_OVSR_MASK | STM32MP13_OVSS_MASK;
+	stm32_adc_clr_bits(adc, STM32H7_ADC_CFGR2, msk);
+
+	if (!ovs_idx)
+		return;
+
+	/*
+	 * The oversampling ratios [2,4,8,..,256] are mapped on OVSR register values [0,1,...,7].
+	 * OVSR = ovs_idx - 1
+	 * These ratio increase the resolution by ovs_idx bits. Apply a right shift to keep initial
+	 * resolution given by "assigned-resolution-bits" property.
+	 * OVSS = ovs_idx
+	 */
+	bits = STM32H7_ROVSE | STM32MP13_OVSS(ovs_idx);
+	if (ovs_idx - 1)
+		bits |= STM32MP13_OVSR(ovs_idx - 1);
+
+	stm32_adc_set_bits(adc, STM32H7_ADC_CFGR2, bits & msk);
 }
 
 static int stm32h7_adc_exit_pwr_down(struct iio_dev *indio_dev)
···
 	return ret;
 }
 
+static int stm32_adc_write_raw(struct iio_dev *indio_dev,
+			       struct iio_chan_spec const *chan,
+			       int val, int val2, long mask)
+{
+	struct stm32_adc *adc = iio_priv(indio_dev);
+	struct device *dev = indio_dev->dev.parent;
+	int nb = adc->cfg->adc_info->num_ovs;
+	unsigned int idx;
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
+		if (val2)
+			return -EINVAL;
+
+		for (idx = 0; idx < nb; idx++)
+			if (adc->cfg->adc_info->oversampling[idx] == val)
+				break;
+		if (idx >= nb)
+			return -EINVAL;
+
+		if (!iio_device_claim_direct(indio_dev))
+			return -EBUSY;
+
+		ret = pm_runtime_resume_and_get(dev);
+		if (ret < 0)
+			goto err;
+
+		adc->cfg->set_ovs(indio_dev, idx);
+
+		pm_runtime_mark_last_busy(dev);
+		pm_runtime_put_autosuspend(dev);
+
+		adc->ovs_idx = idx;
+
+err:
+		iio_device_release_direct(indio_dev);
+
+		return ret;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int stm32_adc_read_avail(struct iio_dev *indio_dev,
+				struct iio_chan_spec const *chan,
+				const int **vals, int *type, int *length, long m)
+{
+	struct stm32_adc *adc = iio_priv(indio_dev);
+
+	switch (m) {
+	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
+		*type = IIO_VAL_INT;
+		*length = adc->cfg->adc_info->num_ovs;
+		*vals = adc->cfg->adc_info->oversampling;
+		return IIO_AVAIL_LIST;
+	default:
+		return -EINVAL;
+	}
+}
+
 static int stm32_adc_read_raw(struct iio_dev *indio_dev,
 			      struct iio_chan_spec const *chan,
 			      int *val, int *val2, long mask)
···
 			*val = -((1 << chan->scan_type.realbits) / 2);
 		else
 			*val = 0;
+		return IIO_VAL_INT;
+
+	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
+		*val = adc->cfg->adc_info->oversampling[adc->ovs_idx];
 		return IIO_VAL_INT;
 
 	default:
···
 
 static const struct iio_info stm32_adc_iio_info = {
 	.read_raw = stm32_adc_read_raw,
+	.write_raw = stm32_adc_write_raw,
+	.read_avail = stm32_adc_read_avail,
 	.validate_trigger = stm32_adc_validate_trigger,
 	.hwfifo_set_watermark = stm32_adc_set_watermark,
 	.update_scan_mode = stm32_adc_update_scan_mode,
···
 		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);
+	if (adc->cfg->has_oversampling) {
+		chan->info_mask_shared_by_all |= BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO);
+		chan->info_mask_shared_by_all_available = BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO);
+	}
 	chan->scan_type.sign = 'u';
 	chan->scan_type.realbits = adc->cfg->adc_info->resolutions[adc->res];
 	chan->scan_type.storagebits = 16;
···
 	.has_boostmode = true,
 	.has_linearcal = true,
 	.has_presel = true,
+	.has_oversampling = true,
 	.start_conv = stm32h7_adc_start_conv,
 	.stop_conv = stm32h7_adc_stop_conv,
 	.prepare = stm32h7_adc_prepare,
···
 	.smp_cycles = stm32h7_adc_smp_cycles,
 	.irq_clear = stm32h7_adc_irq_clear,
 	.ts_int_ch = stm32_adc_min_ts_h7,
+	.set_ovs = stm32h7_adc_set_ovs,
 };
 
 static const unsigned int stm32_adc_min_ts_mp1[] = { 100, 100, 100, 4300, 9800 };
···
 	.has_boostmode = true,
 	.has_linearcal = true,
 	.has_presel = true,
+	.has_oversampling = true,
 	.start_conv = stm32h7_adc_start_conv,
 	.stop_conv = stm32h7_adc_stop_conv,
 	.prepare = stm32h7_adc_prepare,
···
 	.smp_cycles = stm32h7_adc_smp_cycles,
 	.irq_clear = stm32h7_adc_irq_clear,
 	.ts_int_ch = stm32_adc_min_ts_mp1,
+	.set_ovs = stm32h7_adc_set_ovs,
 };
 
 static const unsigned int stm32_adc_min_ts_mp13[] = { 100, 0, 0, 4300, 9800 };
···
 	.regs = &stm32mp13_adc_regspec,
 	.adc_info = &stm32mp13_adc_info,
 	.trigs = stm32h7_adc_trigs,
+	.has_oversampling = true,
 	.start_conv = stm32mp13_adc_start_conv,
 	.stop_conv = stm32h7_adc_stop_conv,
 	.prepare = stm32h7_adc_prepare,
···
 	.smp_cycles = stm32mp13_adc_smp_cycles,
 	.irq_clear = stm32h7_adc_irq_clear,
 	.ts_int_ch = stm32_adc_min_ts_mp13,
+	.set_ovs = stm32mp13_adc_set_ovs,
 };
 
 static const struct of_device_id stm32_adc_of_match[] = {