iio: adc: meson-saradc: add support for the chip's temperature sensor

Channel 6 of the SAR ADC can be switched between two inputs:
SAR_ADC_CH6 input (an actual pad on the SoC) and the signal from the
temperature sensor inside the SoC.

To get usable results from the temperature sensor we need to read the
corresponding calibration data from the eFuse and pass it to the SAR ADC
registers. If the temperature sensor is not calibrated (the eFuse data
contains a bit for this) then the driver will only register the
iio_chan_spec's for voltage measurements.

This only enables the temperature sensor for the Meson8 SoC. Meson8b and
Meson8m2 SoCs can be supported in the future as well but we first need
a way to pass the fifth TSC (temperature sensor coefficient) bit to the
HHI register area (apart from that the infrastructure as already
implemented for Meson8 can be used). On the 64-bit SoCs (GXBB, GXL and
GXM) the temperature sensor inside SAR ADC is firmware-controlled (by
BL30, we can simply use the SCPI hwmon driver to get the chip
temperature).

To keep the devicetree interface backwards compatible we simply skip the
temperature sensor initialization if no eFuse nvmem cell is passed via
devicetree.

The public documentation for the SAR ADC IP block does not explain how
to use the registers to read the temperature. The logic from this patch
is based on reading and understanding Amlogic's GPL kernel sources.
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/meson_saradc.c

@@ -18,6 +18,7 @@
 #include <linux/io.h>
 #include <linux/iio/iio.h>
 #include <linux/module.h>
+#include <linux/nvmem-consumer.h>
 #include <linux/interrupt.h>
 #include <linux/of.h>
 #include <linux/of_irq.h>
@@ -165,6 +166,14 @@
 
 #define MESON_SAR_ADC_MAX_FIFO_SIZE				32
 #define MESON_SAR_ADC_TIMEOUT					100 /* ms */
+#define MESON_SAR_ADC_VOLTAGE_AND_TEMP_CHANNEL			6
+#define MESON_SAR_ADC_TEMP_OFFSET				27
+
+/* temperature sensor calibration information in eFuse */
+#define MESON_SAR_ADC_EFUSE_BYTES				4
+#define MESON_SAR_ADC_EFUSE_BYTE3_UPPER_ADC_VAL			GENMASK(6, 0)
+#define MESON_SAR_ADC_EFUSE_BYTE3_IS_CALIBRATED			BIT(7)
+
 /* for use with IIO_VAL_INT_PLUS_MICRO */
 #define MILLION							1000000
 
@@ -175,16 +184,25 @@
 	.address = _chan,						\
 	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |			\
 				BIT(IIO_CHAN_INFO_AVERAGE_RAW),		\
-	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) |		\
-				BIT(IIO_CHAN_INFO_CALIBBIAS) |		\
+	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),		\
+	.info_mask_shared_by_all = BIT(IIO_CHAN_INFO_CALIBBIAS) |	\
 				BIT(IIO_CHAN_INFO_CALIBSCALE),		\
 	.datasheet_name = "SAR_ADC_CH"#_chan,				\
 }
 
-/*
- * TODO: the hardware supports IIO_TEMP for channel 6 as well which is
- * currently not supported by this driver.
- */
+#define MESON_SAR_ADC_TEMP_CHAN(_chan) {				\
+	.type = IIO_TEMP,						\
+	.channel = _chan,						\
+	.address = MESON_SAR_ADC_VOLTAGE_AND_TEMP_CHANNEL,		\
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |			\
+				BIT(IIO_CHAN_INFO_AVERAGE_RAW),		\
+	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_OFFSET) |		\
+					BIT(IIO_CHAN_INFO_SCALE),	\
+	.info_mask_shared_by_all = BIT(IIO_CHAN_INFO_CALIBBIAS) |	\
+				BIT(IIO_CHAN_INFO_CALIBSCALE),		\
+	.datasheet_name = "TEMP_SENSOR",				\
+}
+
 static const struct iio_chan_spec meson_sar_adc_iio_channels[] = {
 	MESON_SAR_ADC_CHAN(0),
 	MESON_SAR_ADC_CHAN(1),
@@ -197,6 +215,19 @@ static const struct iio_chan_spec meson_sar_adc_iio_channels[] = {
 	IIO_CHAN_SOFT_TIMESTAMP(8),
 };
 
+static const struct iio_chan_spec meson_sar_adc_and_temp_iio_channels[] = {
+	MESON_SAR_ADC_CHAN(0),
+	MESON_SAR_ADC_CHAN(1),
+	MESON_SAR_ADC_CHAN(2),
+	MESON_SAR_ADC_CHAN(3),
+	MESON_SAR_ADC_CHAN(4),
+	MESON_SAR_ADC_CHAN(5),
+	MESON_SAR_ADC_CHAN(6),
+	MESON_SAR_ADC_CHAN(7),
+	MESON_SAR_ADC_TEMP_CHAN(8),
+	IIO_CHAN_SOFT_TIMESTAMP(9),
+};
+
 enum meson_sar_adc_avg_mode {
 	NO_AVERAGING = 0x0,
 	MEAN_AVERAGING = 0x1,
@@ -225,6 +256,9 @@ struct meson_sar_adc_param {
 	u32					bandgap_reg;
 	unsigned int				resolution;
 	const struct regmap_config		*regmap_config;
+	u8					temperature_trimming_bits;
+	unsigned int				temperature_multiplier;
+	unsigned int				temperature_divider;
 };
 
 struct meson_sar_adc_data {
@@ -246,6 +280,9 @@ struct meson_sar_adc_priv {
 	struct completion			done;
 	int					calibbias;
 	int					calibscale;
+	bool					temperature_sensor_calibrated;
+	u8					temperature_sensor_coefficient;
+	u16					temperature_sensor_adc_val;
 };
 
 static const struct regmap_config meson_sar_adc_regmap_config_gxbb = {
@@ -389,9 +426,16 @@ static void meson_sar_adc_enable_channel(struct iio_dev *indio_dev,
 			   MESON_SAR_ADC_DETECT_IDLE_SW_IDLE_MUX_SEL_MASK,
 			   regval);
 
-	if (chan->address == 6)
-		regmap_update_bits(priv->regmap, MESON_SAR_ADC_DELTA_10,
-				   MESON_SAR_ADC_DELTA_10_TEMP_SEL, 0);
+	if (chan->address == MESON_SAR_ADC_VOLTAGE_AND_TEMP_CHANNEL) {
+		if (chan->type == IIO_TEMP)
+			regval = MESON_SAR_ADC_DELTA_10_TEMP_SEL;
+		else
+			regval = 0;
+
+		regmap_update_bits(priv->regmap,
+				   MESON_SAR_ADC_DELTA_10,
+				   MESON_SAR_ADC_DELTA_10_TEMP_SEL, regval);
+	}
 }
 
 static void meson_sar_adc_set_chan7_mux(struct iio_dev *indio_dev,
@@ -506,8 +550,12 @@ static int meson_sar_adc_get_sample(struct iio_dev *indio_dev,
 				    enum meson_sar_adc_num_samples avg_samples,
 				    int *val)
 {
+	struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
 	int ret;
 
+	if (chan->type == IIO_TEMP && !priv->temperature_sensor_calibrated)
+		return -ENOTSUPP;
+
 	ret = meson_sar_adc_lock(indio_dev);
 	if (ret)
 		return ret;
@@ -555,17 +603,31 @@ static int meson_sar_adc_iio_info_read_raw(struct iio_dev *indio_dev,
 		break;
 
 	case IIO_CHAN_INFO_SCALE:
-		ret = regulator_get_voltage(priv->vref);
-		if (ret < 0) {
-			dev_err(indio_dev->dev.parent,
-				"failed to get vref voltage: %d\n", ret);
-			return ret;
+		if (chan->type == IIO_VOLTAGE) {
+			ret = regulator_get_voltage(priv->vref);
+			if (ret < 0) {
+				dev_err(indio_dev->dev.parent,
+					"failed to get vref voltage: %d\n",
+					ret);
+				return ret;
+			}
+
+			*val = ret / 1000;
+			*val2 = priv->param->resolution;
+			return IIO_VAL_FRACTIONAL_LOG2;
+		} else if (chan->type == IIO_TEMP) {
+			/* SoC specific multiplier and divider */
+			*val = priv->param->temperature_multiplier;
+			*val2 = priv->param->temperature_divider;
+
+			/* celsius to millicelsius */
+			*val *= 1000;
+
+			return IIO_VAL_FRACTIONAL;
+		} else {
+			return -EINVAL;
 		}
 
-		*val = ret / 1000;
-		*val2 = priv->param->resolution;
-		return IIO_VAL_FRACTIONAL_LOG2;
-
 	case IIO_CHAN_INFO_CALIBBIAS:
 		*val = priv->calibbias;
 		return IIO_VAL_INT;
@@ -575,6 +637,13 @@ static int meson_sar_adc_iio_info_read_raw(struct iio_dev *indio_dev,
 		*val2 = priv->calibscale % MILLION;
 		return IIO_VAL_INT_PLUS_MICRO;
 
+	case IIO_CHAN_INFO_OFFSET:
+		*val = DIV_ROUND_CLOSEST(MESON_SAR_ADC_TEMP_OFFSET *
+					 priv->param->temperature_divider,
+					 priv->param->temperature_multiplier);
+		*val -= priv->temperature_sensor_adc_val;
+		return IIO_VAL_INT;
+
 	default:
 		return -EINVAL;
 	}
@@ -625,6 +694,65 @@ static int meson_sar_adc_clk_init(struct iio_dev *indio_dev,
 	return 0;
 }
 
+static int meson_sar_adc_temp_sensor_init(struct iio_dev *indio_dev)
+{
+	struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
+	u8 *buf, trimming_bits, trimming_mask, upper_adc_val;
+	struct nvmem_cell *temperature_calib;
+	size_t read_len;
+	int ret;
+
+	temperature_calib = devm_nvmem_cell_get(&indio_dev->dev,
+						"temperature_calib");
+	if (IS_ERR(temperature_calib)) {
+		ret = PTR_ERR(temperature_calib);
+
+		/*
+		 * leave the temperature sensor disabled if no calibration data
+		 * was passed via nvmem-cells.
+		 */
+		if (ret == -ENODEV)
+			return 0;
+
+		if (ret != -EPROBE_DEFER)
+			dev_err(indio_dev->dev.parent,
+				"failed to get temperature_calib cell\n");
+
+		return ret;
+	}
+
+	read_len = MESON_SAR_ADC_EFUSE_BYTES;
+	buf = nvmem_cell_read(temperature_calib, &read_len);
+	if (IS_ERR(buf)) {
+		dev_err(indio_dev->dev.parent,
+			"failed to read temperature_calib cell\n");
+		return PTR_ERR(buf);
+	} else if (read_len != MESON_SAR_ADC_EFUSE_BYTES) {
+		kfree(buf);
+		dev_err(indio_dev->dev.parent,
+			"invalid read size of temperature_calib cell\n");
+		return -EINVAL;
+	}
+
+	trimming_bits = priv->param->temperature_trimming_bits;
+	trimming_mask = BIT(trimming_bits) - 1;
+
+	priv->temperature_sensor_calibrated =
+		buf[3] & MESON_SAR_ADC_EFUSE_BYTE3_IS_CALIBRATED;
+	priv->temperature_sensor_coefficient = buf[2] & trimming_mask;
+
+	upper_adc_val = FIELD_GET(MESON_SAR_ADC_EFUSE_BYTE3_UPPER_ADC_VAL,
+				  buf[3]);
+
+	priv->temperature_sensor_adc_val = buf[2];
+	priv->temperature_sensor_adc_val |= upper_adc_val << BITS_PER_BYTE;
+	priv->temperature_sensor_adc_val >>= trimming_bits;
+
+	kfree(buf);
+
+	return 0;
+}
+
 static int meson_sar_adc_init(struct iio_dev *indio_dev)
 {
 	struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
@@ -649,10 +777,12 @@ static int meson_sar_adc_init(struct iio_dev *indio_dev)
 
 	meson_sar_adc_stop_sample_engine(indio_dev);
 
-	/* update the channel 6 MUX to select the temperature sensor */
+	/*
+	 * disable this bit as seems to be only relevant for Meson6 (based
+	 * on the vendor driver), which we don't support at the moment.
+	 */
 	regmap_update_bits(priv->regmap, MESON_SAR_ADC_REG0,
-			MESON_SAR_ADC_REG0_ADC_TEMP_SEN_SEL,
-			MESON_SAR_ADC_REG0_ADC_TEMP_SEN_SEL);
+			MESON_SAR_ADC_REG0_ADC_TEMP_SEN_SEL, 0);
 
 	/* disable all channels by default */
 	regmap_write(priv->regmap, MESON_SAR_ADC_CHAN_LIST, 0x0);
@@ -709,6 +839,29 @@ static int meson_sar_adc_init(struct iio_dev *indio_dev)
 	regval |= MESON_SAR_ADC_AUX_SW_XP_DRIVE_SW;
 	regmap_write(priv->regmap, MESON_SAR_ADC_AUX_SW, regval);
 
+	if (priv->temperature_sensor_calibrated) {
+		regmap_update_bits(priv->regmap, MESON_SAR_ADC_DELTA_10,
+				   MESON_SAR_ADC_DELTA_10_TS_REVE1,
+				   MESON_SAR_ADC_DELTA_10_TS_REVE1);
+		regmap_update_bits(priv->regmap, MESON_SAR_ADC_DELTA_10,
+				   MESON_SAR_ADC_DELTA_10_TS_REVE0,
+				   MESON_SAR_ADC_DELTA_10_TS_REVE0);
+
+		/*
+		 * set bits [3:0] of the TSC (temperature sensor coefficient)
+		 * to get the correct values when reading the temperature.
+		 */
+		regval = FIELD_PREP(MESON_SAR_ADC_DELTA_10_TS_C_MASK,
+				    priv->temperature_sensor_coefficient);
+		regmap_update_bits(priv->regmap, MESON_SAR_ADC_DELTA_10,
+				   MESON_SAR_ADC_DELTA_10_TS_C_MASK, regval);
+	} else {
+		regmap_update_bits(priv->regmap, MESON_SAR_ADC_DELTA_10,
+				   MESON_SAR_ADC_DELTA_10_TS_REVE1, 0);
+		regmap_update_bits(priv->regmap, MESON_SAR_ADC_DELTA_10,
+				   MESON_SAR_ADC_DELTA_10_TS_REVE0, 0);
+	}
+
 	ret = clk_set_parent(priv->adc_sel_clk, priv->clkin);
 	if (ret) {
 		dev_err(indio_dev->dev.parent,
@@ -894,6 +1047,17 @@ static const struct meson_sar_adc_param meson_sar_adc_meson8_param = {
 	.bandgap_reg = MESON_SAR_ADC_DELTA_10,
 	.regmap_config = &meson_sar_adc_regmap_config_meson8,
 	.resolution = 10,
+	.temperature_trimming_bits = 4,
+	.temperature_multiplier = 18 * 10000,
+	.temperature_divider = 1024 * 10 * 85,
+};
+
+static const struct meson_sar_adc_param meson_sar_adc_meson8b_param = {
+	.has_bl30_integration = false,
+	.clock_rate = 1150000,
+	.bandgap_reg = MESON_SAR_ADC_DELTA_10,
+	.regmap_config = &meson_sar_adc_regmap_config_meson8,
+	.resolution = 10,
 };
 
 static const struct meson_sar_adc_param meson_sar_adc_gxbb_param = {
@@ -918,12 +1082,12 @@ static const struct meson_sar_adc_data meson_sar_adc_meson8_data = {
 };
 
 static const struct meson_sar_adc_data meson_sar_adc_meson8b_data = {
-	.param = &meson_sar_adc_meson8_param,
+	.param = &meson_sar_adc_meson8b_param,
 	.name = "meson-meson8b-saradc",
 };
 
 static const struct meson_sar_adc_data meson_sar_adc_meson8m2_data = {
-	.param = &meson_sar_adc_meson8_param,
+	.param = &meson_sar_adc_meson8b_param,
 	.name = "meson-meson8m2-saradc",
 };
 
@@ -1009,9 +1173,6 @@ static int meson_sar_adc_probe(struct platform_device *pdev)
 	indio_dev->modes = INDIO_DIRECT_MODE;
 	indio_dev->info = &meson_sar_adc_iio_info;
 
-	indio_dev->channels = meson_sar_adc_iio_channels;
-	indio_dev->num_channels = ARRAY_SIZE(meson_sar_adc_iio_channels);
-
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	base = devm_ioremap_resource(&pdev->dev, res);
 	if (IS_ERR(base))
@@ -1078,6 +1239,22 @@ static int meson_sar_adc_probe(struct platform_device *pdev)
 
 	priv->calibscale = MILLION;
 
+	if (priv->param->temperature_trimming_bits) {
+		ret = meson_sar_adc_temp_sensor_init(indio_dev);
+		if (ret)
+			return ret;
+	}
+
+	if (priv->temperature_sensor_calibrated) {
+		indio_dev->channels = meson_sar_adc_and_temp_iio_channels;
+		indio_dev->num_channels =
+			ARRAY_SIZE(meson_sar_adc_and_temp_iio_channels);
+	} else {
+		indio_dev->channels = meson_sar_adc_iio_channels;
+		indio_dev->num_channels =
+			ARRAY_SIZE(meson_sar_adc_iio_channels);
+	}
+
 	ret = meson_sar_adc_init(indio_dev);
 	if (ret)
 		goto err;