[PATCH v9 5/5] iio: adc: versal-sysmon: add oversampling support

[Salih Erim <salih.erim@amd.com>]

Add support for reading and writing the oversampling ratio through
the IIO oversampling_ratio attribute. The hardware supports averaging
2, 4, 8, or 16 samples, plus a ratio of 1 (no averaging).

Temperature and supply channels share oversampling configuration at
the type level (all temperature channels share one ratio, all supply
channels share another), exposed through info_mask_shared_by_type.

The hardware encoding uses sample_count / 2 in a 4-bit field within
the CONFIG register. Per-channel averaging enable registers must also
be updated to activate or deactivate averaging.

Signed-off-by: Salih Erim <salih.erim@amd.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
---
Changes in v9:
  - Add Reviewed-by tag from Andy Shevchenko
  - No code changes

Changes in v8:
  - Use unsigned int for val parameter and hw_val in both
    osr_write helpers (Andy)
  - Use ~0 instead of ~0U for avg enable bitmask (Andy)

Changes in v7:
  - Split sysmon_osr_write into sysmon_osr_write_temp and
    sysmon_osr_write_supply; caller dispatches with if/else
    on chan->type (Jonathan)
  - Restore HW encoding comment in both helpers; fix
    cross-reference in sysmon_osr_write_supply

Changes in v6:
  - Fix FIELD_PREP indentation in sysmon_osr_write (Andy)
  - unsigned int for loop index in sysmon_write_raw (Andy)

Changes in v5:
  - Remove unneeded parentheses in i * SYSMON_REG_STRIDE (Andy)
  - Use struct regmap *map local variable in
    sysmon_set_avg_enable (Andy)
  - switch instead of redundant if/if on channel_type (Andy)
  - Add CONFIG register readback fence after oversampling update
    to prevent NoC bus hang from posted writes (found during
    hardware stress testing)

Changes in v4:
  - Return directly from sysmon_set_avg_enable calls, remove
    else after early returns, drop unreachable return 0 (Jonathan)
  - Rename mask defines to SYSMON_CONFIG_SUPPLY_OSR and
    SYSMON_CONFIG_TEMP_SAT_OSR (Jonathan)
  - Drop "bits X:Y" from GENMASK comments (Jonathan)
  - Blank lines after if (ret) return ret blocks (Jonathan)
  - Move oversampling read inside guard(mutex) scope

Changes in v3:
  - No changes

Changes in v2:
  - EN_AVG per-channel bitmask registers written with all-ones
    instead of boolean 1 when oversampling is enabled
  - EN_AVG write errors propagated to userspace
  - Oversampling limited to satellite temp and supply channels;
    static temp channels do not participate
  - Oversampling exposes actual sample counts (1,2,4,8,16) to
    userspace with internal HW register translation
  - write_raw_get_fmt returns IIO_VAL_INT for oversampling ratio
  - HW encoding documented (sample_count/2, not log2)
  - oversampling_avail is const int[] (type match fix)
 drivers/iio/adc/versal-sysmon-core.c | 153 ++++++++++++++++++++++++++-
 drivers/iio/adc/versal-sysmon.h      |  17 +++
 2 files changed, 169 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/adc/versal-sysmon-core.c b/drivers/iio/adc/versal-sysmon-core.c
index 19a8edd8919..16f474c1bff 100644
--- a/drivers/iio/adc/versal-sysmon-core.c
+++ b/drivers/iio/adc/versal-sysmon-core.c
@@ -27,6 +27,12 @@
 
 #include "versal-sysmon.h"
 
+/*
+ * Oversampling ratio values exposed to userspace via IIO.
+ * Actual number of samples averaged: 1=none, 2=2x, 4=4x, 8=8x, 16=16x.
+ */
+static const int sysmon_oversampling_avail[] = { 1, 2, 4, 8, 16 };
+
 /* TEMP hysteresis mode bit in SYSMON_TEMP_EV_CFG */
 #define SYSMON_TEMP_HYST_MASK		BIT(1)
 
@@ -165,6 +171,12 @@ static int sysmon_read_raw(struct iio_dev *indio_dev,
 
 	guard(mutex)(&sysmon->lock);
 
+	if (mask == IIO_CHAN_INFO_OVERSAMPLING_RATIO) {
+		*val = (chan->type == IIO_TEMP) ? sysmon->temp_oversampling :
+						 sysmon->supply_oversampling;
+		return IIO_VAL_INT;
+	}
+
 	switch (chan->type) {
 	case IIO_TEMP:
 		if (mask == IIO_CHAN_INFO_SCALE) {
@@ -451,6 +463,132 @@ static int sysmon_write_event_value(struct iio_dev *indio_dev,
 	}
 }
 
+static int sysmon_set_avg_enable(struct sysmon *sysmon,
+				 u32 base, u32 count, u32 val)
+{
+	struct regmap *map = sysmon->regmap;
+	int ret;
+
+	for (unsigned int i = 0; i < count; i++) {
+		ret = regmap_write(map, base + i * SYSMON_REG_STRIDE, val);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static int sysmon_osr_write_temp(struct sysmon *sysmon, unsigned int val)
+{
+	/*
+	 * HW register encoding is sample_count / 2:
+	 * 0=none, 1=2x, 2=4x, 4=8x, 8=16x (not log2-based).
+	 */
+	unsigned int hw_val = val >> 1;
+	unsigned int readback;
+	int ret;
+
+	ret = regmap_update_bits(sysmon->regmap, SYSMON_CONFIG,
+				SYSMON_CONFIG_TEMP_SAT_OSR,
+				FIELD_PREP(SYSMON_CONFIG_TEMP_SAT_OSR, hw_val));
+	if (ret)
+		return ret;
+
+	/*
+	 * Readback fence: the SysMon CONFIG register resides in the
+	 * PMC domain behind the NoC. A posted write may not reach the
+	 * hardware before the next MMIO access. Reading the register
+	 * back forces the interconnect to complete the write, preventing
+	 * a bus hang on the subsequent access.
+	 */
+	regmap_read(sysmon->regmap, SYSMON_CONFIG, &readback);
+
+	return sysmon_set_avg_enable(sysmon, SYSMON_TEMP_EN_AVG_BASE,
+				     SYSMON_TEMP_EN_AVG_COUNT,
+				     hw_val ? ~0 : 0);
+}
+
+static int sysmon_osr_write_supply(struct sysmon *sysmon, unsigned int val)
+{
+	/* HW encoding: sample_count / 2 (see sysmon_osr_write_temp) */
+	unsigned int hw_val = val >> 1;
+	unsigned int readback;
+	int ret;
+
+	ret = regmap_update_bits(sysmon->regmap, SYSMON_CONFIG,
+				SYSMON_CONFIG_SUPPLY_OSR,
+				FIELD_PREP(SYSMON_CONFIG_SUPPLY_OSR, hw_val));
+	if (ret)
+		return ret;
+
+	/* Readback fence -- see sysmon_osr_write_temp for details */
+	regmap_read(sysmon->regmap, SYSMON_CONFIG, &readback);
+
+	return sysmon_set_avg_enable(sysmon, SYSMON_SUPPLY_EN_AVG_BASE,
+				     SYSMON_SUPPLY_EN_AVG_COUNT,
+				     hw_val ? ~0 : 0);
+}
+
+static int sysmon_write_raw(struct iio_dev *indio_dev,
+			    struct iio_chan_spec const *chan,
+			    int val, int val2, long mask)
+{
+	struct sysmon *sysmon = iio_priv(indio_dev);
+	unsigned int i;
+	int ret;
+
+	if (mask != IIO_CHAN_INFO_OVERSAMPLING_RATIO)
+		return -EINVAL;
+
+	for (i = 0; i < ARRAY_SIZE(sysmon_oversampling_avail); i++) {
+		if (val == sysmon_oversampling_avail[i])
+			break;
+	}
+	if (i == ARRAY_SIZE(sysmon_oversampling_avail))
+		return -EINVAL;
+
+	guard(mutex)(&sysmon->lock);
+
+	if (chan->type == IIO_TEMP) {
+		ret = sysmon_osr_write_temp(sysmon, val);
+		if (ret)
+			return ret;
+		sysmon->temp_oversampling = val;
+	} else {
+		ret = sysmon_osr_write_supply(sysmon, val);
+		if (ret)
+			return ret;
+		sysmon->supply_oversampling = val;
+	}
+
+	return 0;
+}
+
+static int sysmon_write_raw_get_fmt(struct iio_dev *indio_dev,
+				    struct iio_chan_spec const *chan,
+				    long mask)
+{
+	if (mask == IIO_CHAN_INFO_OVERSAMPLING_RATIO)
+		return IIO_VAL_INT;
+
+	return -EINVAL;
+}
+
+static int sysmon_read_avail(struct iio_dev *indio_dev,
+			     struct iio_chan_spec const *chan,
+			     const int **vals, int *type,
+			     int *length, long mask)
+{
+	if (mask != IIO_CHAN_INFO_OVERSAMPLING_RATIO)
+		return -EINVAL;
+
+	*vals = sysmon_oversampling_avail;
+	*type = IIO_VAL_INT;
+	*length = ARRAY_SIZE(sysmon_oversampling_avail);
+
+	return IIO_AVAIL_LIST;
+}
+
 static int sysmon_read_label(struct iio_dev *indio_dev,
 			     struct iio_chan_spec const *chan,
 			     char *label)
@@ -463,6 +601,9 @@ static int sysmon_read_label(struct iio_dev *indio_dev,
 
 static const struct iio_info sysmon_iio_info = {
 	.read_raw = sysmon_read_raw,
+	.write_raw = sysmon_write_raw,
+	.write_raw_get_fmt = sysmon_write_raw_get_fmt,
+	.read_avail = sysmon_read_avail,
 	.read_label = sysmon_read_label,
 	.read_event_config = sysmon_read_event_config,
 	.write_event_config = sysmon_write_event_config,
@@ -754,6 +895,10 @@ static int sysmon_parse_fw(struct iio_dev *indio_dev, struct device *dev, int ir
 			.indexed = 1,
 			.address = reg,
 			.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED),
+			.info_mask_shared_by_type =
+				BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
+			.info_mask_shared_by_type_available =
+				BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
 			.event_spec = irq > 0 ?
 				sysmon_supply_events : NULL,
 			.num_event_specs = irq > 0 ?
@@ -785,7 +930,11 @@ static int sysmon_parse_fw(struct iio_dev *indio_dev, struct device *dev, int ir
 			.address = SYSMON_TEMP_SAT_BASE +
 				   (reg - 1) * SYSMON_REG_STRIDE,
 			.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
-			.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),
+			.info_mask_shared_by_type =
+				BIT(IIO_CHAN_INFO_SCALE) |
+				BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
+			.info_mask_shared_by_type_available =
+				BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
 			.datasheet_name = label,
 		};
 	}
@@ -832,6 +981,8 @@ int devm_versal_sysmon_core_probe(struct device *dev, struct regmap *regmap)
 
 	sysmon = iio_priv(indio_dev);
 	sysmon->regmap = regmap;
+	sysmon->temp_oversampling = 1;
+	sysmon->supply_oversampling = 1;
 
 	ret = devm_mutex_init(dev, &sysmon->lock);
 	if (ret)
diff --git a/drivers/iio/adc/versal-sysmon.h b/drivers/iio/adc/versal-sysmon.h
index 9fe2793757a..bb9a75bf71c 100644
--- a/drivers/iio/adc/versal-sysmon.h
+++ b/drivers/iio/adc/versal-sysmon.h
@@ -23,11 +23,13 @@ struct regmap;
 #define SYSMON_IMR			0x0048
 #define SYSMON_IER			0x004C
 #define SYSMON_IDR			0x0050
+#define SYSMON_CONFIG			0x0100
 #define SYSMON_TEMP_MAX			0x1030
 #define SYSMON_TEMP_MIN			0x1034
 #define SYSMON_SUPPLY_BASE		0x1040
 #define SYSMON_ALARM_FLAG		0x1018
 #define SYSMON_ALARM_REG		0x1940
+#define SYSMON_SUPPLY_EN_AVG_BASE	0x1958
 #define SYSMON_TEMP_TH_LOW		0x1970
 #define SYSMON_TEMP_TH_UP		0x1974
 #define SYSMON_SUPPLY_TH_LOW		0x1980
@@ -37,6 +39,7 @@ struct regmap;
 #define SYSMON_TEMP_MAX_MAX		0x1F90
 #define SYSMON_STATUS_RESET		0x1F94
 #define SYSMON_TEMP_SAT_BASE		0x1FAC
+#define SYSMON_TEMP_EN_AVG_BASE		0x24B4
 #define SYSMON_MAX_REG			0x24C0
 
 /* NPI unlock value written to SYSMON_NPI_LOCK */
@@ -53,6 +56,16 @@ struct regmap;
 /* ISR/IMR temperature alarm mask (bit 9) */
 #define SYSMON_TEMP_INTR_MASK		BIT(9)
 
+/* SYSMON_CONFIG: supply oversampling ratio */
+#define SYSMON_CONFIG_SUPPLY_OSR	GENMASK(17, 14)
+
+/* SYSMON_CONFIG: temperature satellite oversampling ratio */
+#define SYSMON_CONFIG_TEMP_SAT_OSR	GENMASK(27, 24)
+
+/* Per-channel averaging enable register counts */
+#define SYSMON_SUPPLY_EN_AVG_COUNT	5
+#define SYSMON_TEMP_EN_AVG_COUNT	2
+
 /* Supply voltage conversion register fields */
 #define SYSMON_MANTISSA_MASK		GENMASK(15, 0)
 #define SYSMON_FMT_MASK			BIT(16)
@@ -77,6 +90,8 @@ struct regmap;
  * @temp_mask: temperature interrupt configuration mask
  * @temp_hysteresis: cached DEVICE_TEMP hysteresis in millicelsius
  * @sysmon_unmask_work: re-enables events after alarm condition clears
+ * @temp_oversampling: current temp oversampling ratio
+ * @supply_oversampling: current supply oversampling ratio
  */
 struct sysmon {
 	struct regmap *regmap;
@@ -96,6 +111,8 @@ struct sysmon {
 	unsigned int temp_mask;
 	int temp_hysteresis;
 	struct delayed_work sysmon_unmask_work;
+	unsigned int temp_oversampling;
+	unsigned int supply_oversampling;
 };
 
 int devm_versal_sysmon_core_probe(struct device *dev, struct regmap *regmap);
-- 
2.48.1