iio: adc: add a driver for the SAR ADC found in Amlogic Meson SoCs

This adds support for the SAR (Successive Approximation Register) ADC
on the Amlogic Meson SoCs.

The code is based on the public S805 (Meson8b) and S905 (GXBB)
datasheets (see [0] and [1]), as well as by reading (various versions
of) the vendor driver and by inspecting the registers on the vendor
kernels of my testing-hardware.

Currently the GXBB, GXL and GXM SoCs are supported. GXBB hardware has
10-bit ADC resolution, while GXL and GXM have 12-bit ADC resolution.
The code was written to support older SoCs (Meson8 and Meson8b) as well,
but due to lack of actual testing-hardware no of_device_id was added for
these.

Two "features" from the vendor driver are currently missing:
- the vendor driver uses channel #7 for calibration (this improves the
  accuracy of the results - in my tests the results were less than 3%
  off without calibration compared to the vendor driver). Adding support
  for this should be easy, but is not required for most applications.
- channel #6 is connected to the SoCs internal temperature sensor.
  Adding support for this is probably not so easy since (based on the
  u-boot sources) most SoC versions are using different registers and
  algorithms for the conversion from "ADC value" to temperature.

Supported by the hardware but currently not supported by the driver:
- reading multiple channels at the same time (the hardware has a FIFO
  buffer which stores multiple results)
- continuous sampling (this would require a way to enable this
  individually because otherwise the ADC would be drawing power
  constantly)
- interrupt support (similar to the vendor driver this new driver is
  polling the results. It is unclear if the IRQ-mode is supported on
  older (Meson6 or Meson8) hardware as well or if there are any errata)

[0]
http://dn.odroid.com/S805/Datasheet/S805_Datasheet%20V0.8%2020150126.pdf
[1] http://dn.odroid.com/S905/DataSheet/S905_Public_Datasheet_V1.1.4.pdf

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Tested-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

3 files changed, 935 insertions, 0 deletions

diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index 5f395d4983ed..e2a64fda99f6 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -399,6 +399,18 @@ config MEN_Z188_ADC
 	  This driver can also be built as a module. If so, the module will be
 	  called men_z188_adc.
 
+config MESON_SARADC
+	tristate "Amlogic Meson SAR ADC driver"
+	default ARCH_MESON
+	depends on OF && COMMON_CLK && (ARCH_MESON || COMPILE_TEST)
+	select REGMAP_MMIO
+	help
+	  Say yes here to build support for the SAR ADC found in Amlogic Meson
+	  SoCs.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called meson_saradc.
+
 config MXS_LRADC
         tristate "Freescale i.MX23/i.MX28 LRADC"
         depends on (ARCH_MXS || COMPILE_TEST) && HAS_IOMEM
diff --git a/drivers/iio/adc/Makefile b/drivers/iio/adc/Makefile
index d27f8475712e..d0012620cd1c 100644
--- a/drivers/iio/adc/Makefile
+++ b/drivers/iio/adc/Makefile
@@ -38,6 +38,7 @@ obj-$(CONFIG_MCP320X) += mcp320x.o
 obj-$(CONFIG_MCP3422) += mcp3422.o
 obj-$(CONFIG_MEDIATEK_MT6577_AUXADC) += mt6577_auxadc.o
 obj-$(CONFIG_MEN_Z188_ADC) += men_z188_adc.o
+obj-$(CONFIG_MESON_SARADC) += meson_saradc.o
 obj-$(CONFIG_MXS_LRADC) += mxs-lradc.o
 obj-$(CONFIG_NAU7802) += nau7802.o
 obj-$(CONFIG_PALMAS_GPADC) += palmas_gpadc.o
diff --git a/drivers/iio/adc/meson_saradc.c b/drivers/iio/adc/meson_saradc.c
new file mode 100644
index 000000000000..89def6034f40
--- /dev/null
+++ b/drivers/iio/adc/meson_saradc.c
@@ -0,0 +1,922 @@
+/*
+ * Amlogic Meson Successive Approximation Register (SAR) A/D Converter
+ *
+ * Copyright (C) 2017 Martin Blumenstingl <martin.blumenstingl@googlemail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/bitfield.h>
+#include <linux/clk.h>
+#include <linux/clk-provider.h>
+#include <linux/delay.h>
+#include <linux/io.h>
+#include <linux/iio/iio.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/regulator/consumer.h>
+
+#define MESON_SAR_ADC_REG0					0x00
+	#define MESON_SAR_ADC_REG0_PANEL_DETECT			BIT(31)
+	#define MESON_SAR_ADC_REG0_BUSY_MASK			GENMASK(30, 28)
+	#define MESON_SAR_ADC_REG0_DELTA_BUSY			BIT(30)
+	#define MESON_SAR_ADC_REG0_AVG_BUSY			BIT(29)
+	#define MESON_SAR_ADC_REG0_SAMPLE_BUSY			BIT(28)
+	#define MESON_SAR_ADC_REG0_FIFO_FULL			BIT(27)
+	#define MESON_SAR_ADC_REG0_FIFO_EMPTY			BIT(26)
+	#define MESON_SAR_ADC_REG0_FIFO_COUNT_MASK		GENMASK(25, 21)
+	#define MESON_SAR_ADC_REG0_ADC_BIAS_CTRL_MASK		GENMASK(20, 19)
+	#define MESON_SAR_ADC_REG0_CURR_CHAN_ID_MASK		GENMASK(18, 16)
+	#define MESON_SAR_ADC_REG0_ADC_TEMP_SEN_SEL		BIT(15)
+	#define MESON_SAR_ADC_REG0_SAMPLING_STOP		BIT(14)
+	#define MESON_SAR_ADC_REG0_CHAN_DELTA_EN_MASK		GENMASK(13, 12)
+	#define MESON_SAR_ADC_REG0_DETECT_IRQ_POL		BIT(10)
+	#define MESON_SAR_ADC_REG0_DETECT_IRQ_EN		BIT(9)
+	#define MESON_SAR_ADC_REG0_FIFO_CNT_IRQ_MASK		GENMASK(8, 4)
+	#define MESON_SAR_ADC_REG0_FIFO_IRQ_EN			BIT(3)
+	#define MESON_SAR_ADC_REG0_SAMPLING_START		BIT(2)
+	#define MESON_SAR_ADC_REG0_CONTINUOUS_EN		BIT(1)
+	#define MESON_SAR_ADC_REG0_SAMPLE_ENGINE_ENABLE		BIT(0)
+
+#define MESON_SAR_ADC_CHAN_LIST					0x04
+	#define MESON_SAR_ADC_CHAN_LIST_MAX_INDEX_MASK		GENMASK(26, 24)
+	#define MESON_SAR_ADC_CHAN_LIST_ENTRY_MASK(_chan)	\
+					(GENMASK(2, 0) << ((_chan) * 3))
+
+#define MESON_SAR_ADC_AVG_CNTL					0x08
+	#define MESON_SAR_ADC_AVG_CNTL_AVG_MODE_SHIFT(_chan)	\
+					(16 + ((_chan) * 2))
+	#define MESON_SAR_ADC_AVG_CNTL_AVG_MODE_MASK(_chan)	\
+					(GENMASK(17, 16) << ((_chan) * 2))
+	#define MESON_SAR_ADC_AVG_CNTL_NUM_SAMPLES_SHIFT(_chan)	\
+					(0 + ((_chan) * 2))
+	#define MESON_SAR_ADC_AVG_CNTL_NUM_SAMPLES_MASK(_chan)	\
+					(GENMASK(1, 0) << ((_chan) * 2))
+
+#define MESON_SAR_ADC_REG3					0x0c
+	#define MESON_SAR_ADC_REG3_CNTL_USE_SC_DLY		BIT(31)
+	#define MESON_SAR_ADC_REG3_CLK_EN			BIT(30)
+	#define MESON_SAR_ADC_REG3_BL30_INITIALIZED		BIT(28)
+	#define MESON_SAR_ADC_REG3_CTRL_CONT_RING_COUNTER_EN	BIT(27)
+	#define MESON_SAR_ADC_REG3_CTRL_SAMPLING_CLOCK_PHASE	BIT(26)
+	#define MESON_SAR_ADC_REG3_CTRL_CHAN7_MUX_SEL_MASK	GENMASK(25, 23)
+	#define MESON_SAR_ADC_REG3_DETECT_EN			BIT(22)
+	#define MESON_SAR_ADC_REG3_ADC_EN			BIT(21)
+	#define MESON_SAR_ADC_REG3_PANEL_DETECT_COUNT_MASK	GENMASK(20, 18)
+	#define MESON_SAR_ADC_REG3_PANEL_DETECT_FILTER_TB_MASK	GENMASK(17, 16)
+	#define MESON_SAR_ADC_REG3_ADC_CLK_DIV_SHIFT		10
+	#define MESON_SAR_ADC_REG3_ADC_CLK_DIV_WIDTH		5
+	#define MESON_SAR_ADC_REG3_BLOCK_DLY_SEL_MASK		GENMASK(9, 8)
+	#define MESON_SAR_ADC_REG3_BLOCK_DLY_MASK		GENMASK(7, 0)
+
+#define MESON_SAR_ADC_DELAY					0x10
+	#define MESON_SAR_ADC_DELAY_INPUT_DLY_SEL_MASK		GENMASK(25, 24)
+	#define MESON_SAR_ADC_DELAY_BL30_BUSY			BIT(15)
+	#define MESON_SAR_ADC_DELAY_KERNEL_BUSY			BIT(14)
+	#define MESON_SAR_ADC_DELAY_INPUT_DLY_CNT_MASK		GENMASK(23, 16)
+	#define MESON_SAR_ADC_DELAY_SAMPLE_DLY_SEL_MASK		GENMASK(9, 8)
+	#define MESON_SAR_ADC_DELAY_SAMPLE_DLY_CNT_MASK		GENMASK(7, 0)
+
+#define MESON_SAR_ADC_LAST_RD					0x14
+	#define MESON_SAR_ADC_LAST_RD_LAST_CHANNEL1_MASK	GENMASK(23, 16)
+	#define MESON_SAR_ADC_LAST_RD_LAST_CHANNEL0_MASK	GENMASK(9, 0)
+
+#define MESON_SAR_ADC_FIFO_RD					0x18
+	#define MESON_SAR_ADC_FIFO_RD_CHAN_ID_MASK		GENMASK(14, 12)
+	#define MESON_SAR_ADC_FIFO_RD_SAMPLE_VALUE_MASK		GENMASK(11, 0)
+
+#define MESON_SAR_ADC_AUX_SW					0x1c
+	#define MESON_SAR_ADC_AUX_SW_MUX_SEL_CHAN_MASK(_chan)	\
+					(GENMASK(10, 8) << (((_chan) - 2) * 2))
+	#define MESON_SAR_ADC_AUX_SW_VREF_P_MUX			BIT(6)
+	#define MESON_SAR_ADC_AUX_SW_VREF_N_MUX			BIT(5)
+	#define MESON_SAR_ADC_AUX_SW_MODE_SEL			BIT(4)
+	#define MESON_SAR_ADC_AUX_SW_YP_DRIVE_SW		BIT(3)
+	#define MESON_SAR_ADC_AUX_SW_XP_DRIVE_SW		BIT(2)
+	#define MESON_SAR_ADC_AUX_SW_YM_DRIVE_SW		BIT(1)
+	#define MESON_SAR_ADC_AUX_SW_XM_DRIVE_SW		BIT(0)
+
+#define MESON_SAR_ADC_CHAN_10_SW				0x20
+	#define MESON_SAR_ADC_CHAN_10_SW_CHAN1_MUX_SEL_MASK	GENMASK(25, 23)
+	#define MESON_SAR_ADC_CHAN_10_SW_CHAN1_VREF_P_MUX	BIT(22)
+	#define MESON_SAR_ADC_CHAN_10_SW_CHAN1_VREF_N_MUX	BIT(21)
+	#define MESON_SAR_ADC_CHAN_10_SW_CHAN1_MODE_SEL		BIT(20)
+	#define MESON_SAR_ADC_CHAN_10_SW_CHAN1_YP_DRIVE_SW	BIT(19)
+	#define MESON_SAR_ADC_CHAN_10_SW_CHAN1_XP_DRIVE_SW	BIT(18)
+	#define MESON_SAR_ADC_CHAN_10_SW_CHAN1_YM_DRIVE_SW	BIT(17)
+	#define MESON_SAR_ADC_CHAN_10_SW_CHAN1_XM_DRIVE_SW	BIT(16)
+	#define MESON_SAR_ADC_CHAN_10_SW_CHAN0_MUX_SEL_MASK	GENMASK(9, 7)
+	#define MESON_SAR_ADC_CHAN_10_SW_CHAN0_VREF_P_MUX	BIT(6)
+	#define MESON_SAR_ADC_CHAN_10_SW_CHAN0_VREF_N_MUX	BIT(5)
+	#define MESON_SAR_ADC_CHAN_10_SW_CHAN0_MODE_SEL		BIT(4)
+	#define MESON_SAR_ADC_CHAN_10_SW_CHAN0_YP_DRIVE_SW	BIT(3)
+	#define MESON_SAR_ADC_CHAN_10_SW_CHAN0_XP_DRIVE_SW	BIT(2)
+	#define MESON_SAR_ADC_CHAN_10_SW_CHAN0_YM_DRIVE_SW	BIT(1)
+	#define MESON_SAR_ADC_CHAN_10_SW_CHAN0_XM_DRIVE_SW	BIT(0)
+
+#define MESON_SAR_ADC_DETECT_IDLE_SW				0x24
+	#define MESON_SAR_ADC_DETECT_IDLE_SW_DETECT_SW_EN	BIT(26)
+	#define MESON_SAR_ADC_DETECT_IDLE_SW_DETECT_MUX_MASK	GENMASK(25, 23)
+	#define MESON_SAR_ADC_DETECT_IDLE_SW_DETECT_VREF_P_MUX	BIT(22)
+	#define MESON_SAR_ADC_DETECT_IDLE_SW_DETECT_VREF_N_MUX	BIT(21)
+	#define MESON_SAR_ADC_DETECT_IDLE_SW_DETECT_MODE_SEL	BIT(20)
+	#define MESON_SAR_ADC_DETECT_IDLE_SW_DETECT_YP_DRIVE_SW	BIT(19)
+	#define MESON_SAR_ADC_DETECT_IDLE_SW_DETECT_XP_DRIVE_SW	BIT(18)
+	#define MESON_SAR_ADC_DETECT_IDLE_SW_DETECT_YM_DRIVE_SW	BIT(17)
+	#define MESON_SAR_ADC_DETECT_IDLE_SW_DETECT_XM_DRIVE_SW	BIT(16)
+	#define MESON_SAR_ADC_DETECT_IDLE_SW_IDLE_MUX_SEL_MASK	GENMASK(9, 7)
+	#define MESON_SAR_ADC_DETECT_IDLE_SW_IDLE_VREF_P_MUX	BIT(6)
+	#define MESON_SAR_ADC_DETECT_IDLE_SW_IDLE_VREF_N_MUX	BIT(5)
+	#define MESON_SAR_ADC_DETECT_IDLE_SW_IDLE_MODE_SEL	BIT(4)
+	#define MESON_SAR_ADC_DETECT_IDLE_SW_IDLE_YP_DRIVE_SW	BIT(3)
+	#define MESON_SAR_ADC_DETECT_IDLE_SW_IDLE_XP_DRIVE_SW	BIT(2)
+	#define MESON_SAR_ADC_DETECT_IDLE_SW_IDLE_YM_DRIVE_SW	BIT(1)
+	#define MESON_SAR_ADC_DETECT_IDLE_SW_IDLE_XM_DRIVE_SW	BIT(0)
+
+#define MESON_SAR_ADC_DELTA_10					0x28
+	#define MESON_SAR_ADC_DELTA_10_TEMP_SEL			BIT(27)
+	#define MESON_SAR_ADC_DELTA_10_TS_REVE1			BIT(26)
+	#define MESON_SAR_ADC_DELTA_10_CHAN1_DELTA_VALUE_MASK	GENMASK(25, 16)
+	#define MESON_SAR_ADC_DELTA_10_TS_REVE0			BIT(15)
+	#define MESON_SAR_ADC_DELTA_10_TS_C_SHIFT		11
+	#define MESON_SAR_ADC_DELTA_10_TS_C_MASK		GENMASK(14, 11)
+	#define MESON_SAR_ADC_DELTA_10_TS_VBG_EN		BIT(10)
+	#define MESON_SAR_ADC_DELTA_10_CHAN0_DELTA_VALUE_MASK	GENMASK(9, 0)
+
+/*
+ * NOTE: registers from here are undocumented (the vendor Linux kernel driver
+ * and u-boot source served as reference). These only seem to be relevant on
+ * GXBB and newer.
+ */
+#define MESON_SAR_ADC_REG11					0x2c
+	#define MESON_SAR_ADC_REG11_BANDGAP_EN			BIT(13)
+
+#define MESON_SAR_ADC_REG13					0x34
+	#define MESON_SAR_ADC_REG13_12BIT_CALIBRATION_MASK	GENMASK(13, 8)
+
+#define MESON_SAR_ADC_MAX_FIFO_SIZE				32
+
+#define MESON_SAR_ADC_CHAN(_chan) {					\
+	.type = IIO_VOLTAGE,						\
+	.indexed = 1,							\
+	.channel = _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),		\
+	.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.
+ */
+static const struct iio_chan_spec meson_sar_adc_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),
+	IIO_CHAN_SOFT_TIMESTAMP(8),
+};
+
+enum meson_sar_adc_avg_mode {
+	NO_AVERAGING = 0x0,
+	MEAN_AVERAGING = 0x1,
+	MEDIAN_AVERAGING = 0x2,
+};
+
+enum meson_sar_adc_num_samples {
+	ONE_SAMPLE = 0x0,
+	TWO_SAMPLES = 0x1,
+	FOUR_SAMPLES = 0x2,
+	EIGHT_SAMPLES = 0x3,
+};
+
+enum meson_sar_adc_chan7_mux_sel {
+	CHAN7_MUX_VSS = 0x0,
+	CHAN7_MUX_VDD_DIV4 = 0x1,
+	CHAN7_MUX_VDD_DIV2 = 0x2,
+	CHAN7_MUX_VDD_MUL3_DIV4 = 0x3,
+	CHAN7_MUX_VDD = 0x4,
+	CHAN7_MUX_CH7_INPUT = 0x7,
+};
+
+struct meson_sar_adc_data {
+	unsigned int				resolution;
+	const char				*name;
+};
+
+struct meson_sar_adc_priv {
+	struct regmap				*regmap;
+	struct regulator			*vref;
+	const struct meson_sar_adc_data		*data;
+	struct clk				*clkin;
+	struct clk				*core_clk;
+	struct clk				*sana_clk;
+	struct clk				*adc_sel_clk;
+	struct clk				*adc_clk;
+	struct clk_gate				clk_gate;
+	struct clk				*adc_div_clk;
+	struct clk_divider			clk_div;
+};
+
+static const struct regmap_config meson_sar_adc_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 32,
+	.reg_stride = 4,
+	.max_register = MESON_SAR_ADC_REG13,
+};
+
+static unsigned int meson_sar_adc_get_fifo_count(struct iio_dev *indio_dev)
+{
+	struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
+	u32 regval;
+
+	regmap_read(priv->regmap, MESON_SAR_ADC_REG0, &regval);
+
+	return FIELD_GET(MESON_SAR_ADC_REG0_FIFO_COUNT_MASK, regval);
+}
+
+static int meson_sar_adc_wait_busy_clear(struct iio_dev *indio_dev)
+{
+	struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
+	int regval, timeout = 10000;
+
+	/*
+	 * NOTE: we need a small delay before reading the status, otherwise
+	 * the sample engine may not have started internally (which would
+	 * seem to us that sampling is already finished).
+	 */
+	do {
+		udelay(1);
+		regmap_read(priv->regmap, MESON_SAR_ADC_REG0, &regval);
+	} while (FIELD_GET(MESON_SAR_ADC_REG0_BUSY_MASK, regval) && timeout--);
+
+	if (timeout < 0)
+		return -ETIMEDOUT;
+
+	return 0;
+}
+
+static int meson_sar_adc_read_raw_sample(struct iio_dev *indio_dev,
+					 const struct iio_chan_spec *chan,
+					 int *val)
+{
+	struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
+	int ret, regval, fifo_chan, fifo_val, sum = 0, count = 0;
+
+	ret = meson_sar_adc_wait_busy_clear(indio_dev);
+	if (ret)
+		return ret;
+
+	while (meson_sar_adc_get_fifo_count(indio_dev) > 0 &&
+	       count < MESON_SAR_ADC_MAX_FIFO_SIZE) {
+		regmap_read(priv->regmap, MESON_SAR_ADC_FIFO_RD, &regval);
+
+		fifo_chan = FIELD_GET(MESON_SAR_ADC_FIFO_RD_CHAN_ID_MASK,
+				      regval);
+		if (fifo_chan != chan->channel)
+			continue;
+
+		fifo_val = FIELD_GET(MESON_SAR_ADC_FIFO_RD_SAMPLE_VALUE_MASK,
+				     regval);
+		fifo_val &= (BIT(priv->data->resolution) - 1);
+
+		sum += fifo_val;
+		count++;
+	}
+
+	if (!count)
+		return -ENOENT;
+
+	*val = sum / count;
+
+	return 0;
+}
+
+static void meson_sar_adc_set_averaging(struct iio_dev *indio_dev,
+					const struct iio_chan_spec *chan,
+					enum meson_sar_adc_avg_mode mode,
+					enum meson_sar_adc_num_samples samples)
+{
+	struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
+	int val, channel = chan->channel;
+
+	val = samples << MESON_SAR_ADC_AVG_CNTL_NUM_SAMPLES_SHIFT(channel);
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_AVG_CNTL,
+			   MESON_SAR_ADC_AVG_CNTL_NUM_SAMPLES_MASK(channel),
+			   val);
+
+	val = mode << MESON_SAR_ADC_AVG_CNTL_AVG_MODE_SHIFT(channel);
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_AVG_CNTL,
+			   MESON_SAR_ADC_AVG_CNTL_AVG_MODE_MASK(channel), val);
+}
+
+static void meson_sar_adc_enable_channel(struct iio_dev *indio_dev,
+					const struct iio_chan_spec *chan)
+{
+	struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
+	u32 regval;
+
+	/*
+	 * the SAR ADC engine allows sampling multiple channels at the same
+	 * time. to keep it simple we're only working with one *internal*
+	 * channel, which starts counting at index 0 (which means: count = 1).
+	 */
+	regval = FIELD_PREP(MESON_SAR_ADC_CHAN_LIST_MAX_INDEX_MASK, 0);
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_CHAN_LIST,
+			   MESON_SAR_ADC_CHAN_LIST_MAX_INDEX_MASK, regval);
+
+	/* map channel index 0 to the channel which we want to read */
+	regval = FIELD_PREP(MESON_SAR_ADC_CHAN_LIST_ENTRY_MASK(0),
+			    chan->channel);
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_CHAN_LIST,
+			   MESON_SAR_ADC_CHAN_LIST_ENTRY_MASK(0), regval);
+
+	regval = FIELD_PREP(MESON_SAR_ADC_DETECT_IDLE_SW_DETECT_MUX_MASK,
+			    chan->channel);
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_DETECT_IDLE_SW,
+			   MESON_SAR_ADC_DETECT_IDLE_SW_DETECT_MUX_MASK,
+			   regval);
+
+	regval = FIELD_PREP(MESON_SAR_ADC_DETECT_IDLE_SW_IDLE_MUX_SEL_MASK,
+			    chan->channel);
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_DETECT_IDLE_SW,
+			   MESON_SAR_ADC_DETECT_IDLE_SW_IDLE_MUX_SEL_MASK,
+			   regval);
+
+	if (chan->channel == 6)
+		regmap_update_bits(priv->regmap, MESON_SAR_ADC_DELTA_10,
+				   MESON_SAR_ADC_DELTA_10_TEMP_SEL, 0);
+}
+
+static void meson_sar_adc_set_chan7_mux(struct iio_dev *indio_dev,
+					enum meson_sar_adc_chan7_mux_sel sel)
+{
+	struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
+	u32 regval;
+
+	regval = FIELD_PREP(MESON_SAR_ADC_REG3_CTRL_CHAN7_MUX_SEL_MASK, sel);
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_REG3,
+			   MESON_SAR_ADC_REG3_CTRL_CHAN7_MUX_SEL_MASK, regval);
+
+	usleep_range(10, 20);
+}
+
+static void meson_sar_adc_start_sample_engine(struct iio_dev *indio_dev)
+{
+	struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
+
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_REG0,
+			   MESON_SAR_ADC_REG0_SAMPLE_ENGINE_ENABLE,
+			   MESON_SAR_ADC_REG0_SAMPLE_ENGINE_ENABLE);
+
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_REG0,
+			   MESON_SAR_ADC_REG0_SAMPLING_START,
+			   MESON_SAR_ADC_REG0_SAMPLING_START);
+}
+
+static void meson_sar_adc_stop_sample_engine(struct iio_dev *indio_dev)
+{
+	struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
+
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_REG0,
+			   MESON_SAR_ADC_REG0_SAMPLING_STOP,
+			   MESON_SAR_ADC_REG0_SAMPLING_STOP);
+
+	/* wait until all modules are stopped */
+	meson_sar_adc_wait_busy_clear(indio_dev);
+
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_REG0,
+			   MESON_SAR_ADC_REG0_SAMPLE_ENGINE_ENABLE, 0);
+}
+
+static int meson_sar_adc_lock(struct iio_dev *indio_dev)
+{
+	struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
+	int val, timeout = 10000;
+
+	mutex_lock(&indio_dev->mlock);
+
+	/* prevent BL30 from using the SAR ADC while we are using it */
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_DELAY,
+			   MESON_SAR_ADC_DELAY_KERNEL_BUSY,
+			   MESON_SAR_ADC_DELAY_KERNEL_BUSY);
+
+	/* wait until BL30 releases it's lock (so we can use the SAR ADC) */
+	do {
+		udelay(1);
+		regmap_read(priv->regmap, MESON_SAR_ADC_DELAY, &val);
+	} while (val & MESON_SAR_ADC_DELAY_BL30_BUSY && timeout--);
+
+	if (timeout < 0)
+		return -ETIMEDOUT;
+
+	return 0;
+}
+
+static void meson_sar_adc_unlock(struct iio_dev *indio_dev)
+{
+	struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
+
+	/* allow BL30 to use the SAR ADC again */
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_DELAY,
+			   MESON_SAR_ADC_DELAY_KERNEL_BUSY, 0);
+
+	mutex_unlock(&indio_dev->mlock);
+}
+
+static void meson_sar_adc_clear_fifo(struct iio_dev *indio_dev)
+{
+	struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
+	int count;
+
+	for (count = 0; count < MESON_SAR_ADC_MAX_FIFO_SIZE; count++) {
+		if (!meson_sar_adc_get_fifo_count(indio_dev))
+			break;
+
+		regmap_read(priv->regmap, MESON_SAR_ADC_FIFO_RD, 0);
+	}
+}
+
+static int meson_sar_adc_get_sample(struct iio_dev *indio_dev,
+				    const struct iio_chan_spec *chan,
+				    enum meson_sar_adc_avg_mode avg_mode,
+				    enum meson_sar_adc_num_samples avg_samples,
+				    int *val)
+{
+	int ret;
+
+	ret = meson_sar_adc_lock(indio_dev);
+	if (ret)
+		return ret;
+
+	/* clear the FIFO to make sure we're not reading old values */
+	meson_sar_adc_clear_fifo(indio_dev);
+
+	meson_sar_adc_set_averaging(indio_dev, chan, avg_mode, avg_samples);
+
+	meson_sar_adc_enable_channel(indio_dev, chan);
+
+	meson_sar_adc_start_sample_engine(indio_dev);
+	ret = meson_sar_adc_read_raw_sample(indio_dev, chan, val);
+	meson_sar_adc_stop_sample_engine(indio_dev);
+
+	meson_sar_adc_unlock(indio_dev);
+
+	if (ret) {
+		dev_warn(indio_dev->dev.parent,
+			 "failed to read sample for channel %d: %d\n",
+			 chan->channel, ret);
+		return ret;
+	}
+
+	return IIO_VAL_INT;
+}
+
+static int meson_sar_adc_iio_info_read_raw(struct iio_dev *indio_dev,
+					   const struct iio_chan_spec *chan,
+					   int *val, int *val2, long mask)
+{
+	struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		return meson_sar_adc_get_sample(indio_dev, chan, NO_AVERAGING,
+						ONE_SAMPLE, val);
+		break;
+
+	case IIO_CHAN_INFO_AVERAGE_RAW:
+		return meson_sar_adc_get_sample(indio_dev, chan,
+						MEAN_AVERAGING, EIGHT_SAMPLES,
+						val);
+		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;
+		}
+
+		*val = ret / 1000;
+		*val2 = priv->data->resolution;
+		return IIO_VAL_FRACTIONAL_LOG2;
+
+	default:
+		return -EINVAL;
+	}
+}
+
+static int meson_sar_adc_clk_init(struct iio_dev *indio_dev,
+				  void __iomem *base)
+{
+	struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
+	struct clk_init_data init;
+	const char *clk_parents[1];
+
+	init.name = devm_kasprintf(&indio_dev->dev, GFP_KERNEL, "%s#adc_div",
+				   of_node_full_name(indio_dev->dev.of_node));
+	init.flags = 0;
+	init.ops = &clk_divider_ops;
+	clk_parents[0] = __clk_get_name(priv->clkin);
+	init.parent_names = clk_parents;
+	init.num_parents = 1;
+
+	priv->clk_div.reg = base + MESON_SAR_ADC_REG3;
+	priv->clk_div.shift = MESON_SAR_ADC_REG3_ADC_CLK_DIV_SHIFT;
+	priv->clk_div.width = MESON_SAR_ADC_REG3_ADC_CLK_DIV_WIDTH;
+	priv->clk_div.hw.init = &init;
+	priv->clk_div.flags = 0;
+
+	priv->adc_div_clk = devm_clk_register(&indio_dev->dev,
+					      &priv->clk_div.hw);
+	if (WARN_ON(IS_ERR(priv->adc_div_clk)))
+		return PTR_ERR(priv->adc_div_clk);
+
+	init.name = devm_kasprintf(&indio_dev->dev, GFP_KERNEL, "%s#adc_en",
+				   of_node_full_name(indio_dev->dev.of_node));
+	init.flags = CLK_SET_RATE_PARENT;
+	init.ops = &clk_gate_ops;
+	clk_parents[0] = __clk_get_name(priv->adc_div_clk);
+	init.parent_names = clk_parents;
+	init.num_parents = 1;
+
+	priv->clk_gate.reg = base + MESON_SAR_ADC_REG3;
+	priv->clk_gate.bit_idx = fls(MESON_SAR_ADC_REG3_CLK_EN);
+	priv->clk_gate.hw.init = &init;
+
+	priv->adc_clk = devm_clk_register(&indio_dev->dev, &priv->clk_gate.hw);
+	if (WARN_ON(IS_ERR(priv->adc_clk)))
+		return PTR_ERR(priv->adc_clk);
+
+	return 0;
+}
+
+static int meson_sar_adc_init(struct iio_dev *indio_dev)
+{
+	struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
+	int regval, ret;
+
+	/*
+	 * make sure we start at CH7 input since the other muxes are only used
+	 * for internal calibration.
+	 */
+	meson_sar_adc_set_chan7_mux(indio_dev, CHAN7_MUX_CH7_INPUT);
+
+	/*
+	 * leave sampling delay and the input clocks as configured by BL30 to
+	 * make sure BL30 gets the values it expects when reading the
+	 * temperature sensor.
+	 */
+	regmap_read(priv->regmap, MESON_SAR_ADC_REG3, &regval);
+	if (regval & MESON_SAR_ADC_REG3_BL30_INITIALIZED)
+		return 0;
+
+	meson_sar_adc_stop_sample_engine(indio_dev);
+
+	/* update the channel 6 MUX to select the temperature sensor */
+	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);
+
+	/* disable all channels by default */
+	regmap_write(priv->regmap, MESON_SAR_ADC_CHAN_LIST, 0x0);
+
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_REG3,
+			   MESON_SAR_ADC_REG3_CTRL_SAMPLING_CLOCK_PHASE, 0);
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_REG3,
+			   MESON_SAR_ADC_REG3_CNTL_USE_SC_DLY,
+			   MESON_SAR_ADC_REG3_CNTL_USE_SC_DLY);
+
+	/* delay between two samples = (10+1) * 1uS */
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_DELAY,
+			   MESON_SAR_ADC_DELAY_INPUT_DLY_CNT_MASK,
+			   FIELD_PREP(MESON_SAR_ADC_DELAY_SAMPLE_DLY_CNT_MASK,
+				      10));
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_DELAY,
+			   MESON_SAR_ADC_DELAY_SAMPLE_DLY_SEL_MASK,
+			   FIELD_PREP(MESON_SAR_ADC_DELAY_SAMPLE_DLY_SEL_MASK,
+				      0));
+
+	/* delay between two samples = (10+1) * 1uS */
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_DELAY,
+			   MESON_SAR_ADC_DELAY_INPUT_DLY_CNT_MASK,
+			   FIELD_PREP(MESON_SAR_ADC_DELAY_INPUT_DLY_CNT_MASK,
+				      10));
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_DELAY,
+			   MESON_SAR_ADC_DELAY_INPUT_DLY_SEL_MASK,
+			   FIELD_PREP(MESON_SAR_ADC_DELAY_INPUT_DLY_SEL_MASK,
+				      1));
+
+	ret = clk_set_parent(priv->adc_sel_clk, priv->clkin);
+	if (ret) {
+		dev_err(indio_dev->dev.parent,
+			"failed to set adc parent to clkin\n");
+		return ret;
+	}
+
+	ret = clk_set_rate(priv->adc_clk, 1200000);
+	if (ret) {
+		dev_err(indio_dev->dev.parent,
+			"failed to set adc clock rate\n");
+		return ret;
+	}
+
+	return 0;
+}
+
+static int meson_sar_adc_hw_enable(struct iio_dev *indio_dev)
+{
+	struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
+	int ret;
+
+	ret = meson_sar_adc_lock(indio_dev);
+	if (ret)
+		goto err_lock;
+
+	ret = regulator_enable(priv->vref);
+	if (ret < 0) {
+		dev_err(indio_dev->dev.parent,
+			"failed to enable vref regulator\n");
+		goto err_vref;
+	}
+
+	ret = clk_prepare_enable(priv->core_clk);
+	if (ret) {
+		dev_err(indio_dev->dev.parent, "failed to enable core clk\n");
+		goto err_core_clk;
+	}
+
+	ret = clk_prepare_enable(priv->sana_clk);
+	if (ret) {
+		dev_err(indio_dev->dev.parent, "failed to enable sana clk\n");
+		goto err_sana_clk;
+	}
+
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_REG11,
+			   MESON_SAR_ADC_REG11_BANDGAP_EN,
+			   MESON_SAR_ADC_REG11_BANDGAP_EN);
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_REG3,
+			   MESON_SAR_ADC_REG3_ADC_EN,
+			   MESON_SAR_ADC_REG3_ADC_EN);
+
+	udelay(5);
+
+	ret = clk_prepare_enable(priv->adc_clk);
+	if (ret) {
+		dev_err(indio_dev->dev.parent, "failed to enable adc clk\n");
+		goto err_adc_clk;
+	}
+
+	meson_sar_adc_unlock(indio_dev);
+
+	return 0;
+
+err_adc_clk:
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_REG3,
+			   MESON_SAR_ADC_REG3_ADC_EN, 0);
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_REG11,
+			   MESON_SAR_ADC_REG11_BANDGAP_EN, 0);
+	clk_disable_unprepare(priv->sana_clk);
+err_sana_clk:
+	clk_disable_unprepare(priv->core_clk);
+err_core_clk:
+	regulator_disable(priv->vref);
+err_vref:
+	meson_sar_adc_unlock(indio_dev);
+err_lock:
+	return ret;
+}
+
+static int meson_sar_adc_hw_disable(struct iio_dev *indio_dev)
+{
+	struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
+	int ret;
+
+	ret = meson_sar_adc_lock(indio_dev);
+	if (ret)
+		return ret;
+
+	clk_disable_unprepare(priv->adc_clk);
+
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_REG3,
+			   MESON_SAR_ADC_REG3_ADC_EN, 0);
+	regmap_update_bits(priv->regmap, MESON_SAR_ADC_REG11,
+			   MESON_SAR_ADC_REG11_BANDGAP_EN, 0);
+
+	clk_disable_unprepare(priv->sana_clk);
+	clk_disable_unprepare(priv->core_clk);
+
+	regulator_disable(priv->vref);
+
+	meson_sar_adc_unlock(indio_dev);
+
+	return 0;
+}
+
+static const struct iio_info meson_sar_adc_iio_info = {
+	.read_raw = meson_sar_adc_iio_info_read_raw,
+	.driver_module = THIS_MODULE,
+};
+
+struct meson_sar_adc_data meson_sar_adc_gxbb_data = {
+	.resolution = 10,
+	.name = "meson-gxbb-saradc",
+};
+
+struct meson_sar_adc_data meson_sar_adc_gxl_data = {
+	.resolution = 12,
+	.name = "meson-gxl-saradc",
+};
+
+struct meson_sar_adc_data meson_sar_adc_gxm_data = {
+	.resolution = 12,
+	.name = "meson-gxm-saradc",
+};
+
+static const struct of_device_id meson_sar_adc_of_match[] = {
+	{
+		.compatible = "amlogic,meson-gxbb-saradc",
+		.data = &meson_sar_adc_gxbb_data,
+	}, {
+		.compatible = "amlogic,meson-gxl-saradc",
+		.data = &meson_sar_adc_gxl_data,
+	}, {
+		.compatible = "amlogic,meson-gxm-saradc",
+		.data = &meson_sar_adc_gxm_data,
+	},
+	{},
+};
+MODULE_DEVICE_TABLE(of, meson_sar_adc_of_match);
+
+static int meson_sar_adc_probe(struct platform_device *pdev)
+{
+	struct meson_sar_adc_priv *priv;
+	struct iio_dev *indio_dev;
+	struct resource *res;
+	void __iomem *base;
+	const struct of_device_id *match;
+	int ret;
+
+	indio_dev = devm_iio_device_alloc(&pdev->dev, sizeof(*priv));
+	if (!indio_dev) {
+		dev_err(&pdev->dev, "failed allocating iio device\n");
+		return -ENOMEM;
+	}
+
+	priv = iio_priv(indio_dev);
+
+	match = of_match_device(meson_sar_adc_of_match, &pdev->dev);
+	priv->data = match->data;
+
+	indio_dev->name = priv->data->name;
+	indio_dev->dev.parent = &pdev->dev;
+	indio_dev->dev.of_node = pdev->dev.of_node;
+	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))
+		return PTR_ERR(base);
+
+	priv->regmap = devm_regmap_init_mmio(&pdev->dev, base,
+					     &meson_sar_adc_regmap_config);
+	if (IS_ERR(priv->regmap))
+		return PTR_ERR(priv->regmap);
+
+	priv->clkin = devm_clk_get(&pdev->dev, "clkin");
+	if (IS_ERR(priv->clkin)) {
+		dev_err(&pdev->dev, "failed to get clkin\n");
+		return PTR_ERR(priv->clkin);
+	}
+
+	priv->core_clk = devm_clk_get(&pdev->dev, "core");
+	if (IS_ERR(priv->core_clk)) {
+		dev_err(&pdev->dev, "failed to get core clk\n");
+		return PTR_ERR(priv->core_clk);
+	}
+
+	priv->sana_clk = devm_clk_get(&pdev->dev, "sana");
+	if (IS_ERR(priv->sana_clk)) {
+		if (PTR_ERR(priv->sana_clk) == -ENOENT) {
+			priv->sana_clk = NULL;
+		} else {
+			dev_err(&pdev->dev, "failed to get sana clk\n");
+			return PTR_ERR(priv->sana_clk);
+		}
+	}
+
+	priv->adc_clk = devm_clk_get(&pdev->dev, "adc_clk");
+	if (IS_ERR(priv->adc_clk)) {
+		if (PTR_ERR(priv->adc_clk) == -ENOENT) {
+			priv->adc_clk = NULL;
+		} else {
+			dev_err(&pdev->dev, "failed to get adc clk\n");
+			return PTR_ERR(priv->adc_clk);
+		}
+	}
+
+	priv->adc_sel_clk = devm_clk_get(&pdev->dev, "adc_sel");
+	if (IS_ERR(priv->adc_sel_clk)) {
+		if (PTR_ERR(priv->adc_sel_clk) == -ENOENT) {
+			priv->adc_sel_clk = NULL;
+		} else {
+			dev_err(&pdev->dev, "failed to get adc_sel clk\n");
+			return PTR_ERR(priv->adc_sel_clk);
+		}
+	}
+
+	/* on pre-GXBB SoCs the SAR ADC itself provides the ADC clock: */
+	if (!priv->adc_clk) {
+		ret = meson_sar_adc_clk_init(indio_dev, base);
+		if (ret)
+			return ret;
+	}
+
+	priv->vref = devm_regulator_get(&pdev->dev, "vref");
+	if (IS_ERR(priv->vref)) {
+		dev_err(&pdev->dev, "failed to get vref regulator\n");
+		return PTR_ERR(priv->vref);
+	}
+
+	ret = meson_sar_adc_init(indio_dev);
+	if (ret)
+		goto err;
+
+	ret = meson_sar_adc_hw_enable(indio_dev);
+	if (ret)
+		goto err;
+
+	platform_set_drvdata(pdev, indio_dev);
+
+	ret = iio_device_register(indio_dev);
+	if (ret)
+		goto err_hw;
+
+	return 0;
+
+err_hw:
+	meson_sar_adc_hw_disable(indio_dev);
+err:
+	return ret;
+}
+
+static int meson_sar_adc_remove(struct platform_device *pdev)
+{
+	struct iio_dev *indio_dev = platform_get_drvdata(pdev);
+
+	iio_device_unregister(indio_dev);
+
+	return meson_sar_adc_hw_disable(indio_dev);
+}
+
+static int __maybe_unused meson_sar_adc_suspend(struct device *dev)
+{
+	struct iio_dev *indio_dev = dev_get_drvdata(dev);
+
+	return meson_sar_adc_hw_disable(indio_dev);
+}
+
+static int __maybe_unused meson_sar_adc_resume(struct device *dev)
+{
+	struct iio_dev *indio_dev = dev_get_drvdata(dev);
+
+	return meson_sar_adc_hw_enable(indio_dev);
+}
+
+static SIMPLE_DEV_PM_OPS(meson_sar_adc_pm_ops,
+			 meson_sar_adc_suspend, meson_sar_adc_resume);
+
+static struct platform_driver meson_sar_adc_driver = {
+	.probe		= meson_sar_adc_probe,
+	.remove		= meson_sar_adc_remove,
+	.driver		= {
+		.name	= "meson-saradc",
+		.of_match_table = meson_sar_adc_of_match,
+		.pm = &meson_sar_adc_pm_ops,
+	},
+};
+
+module_platform_driver(meson_sar_adc_driver);
+
+MODULE_AUTHOR("Martin Blumenstingl <martin.blumenstingl@googlemail.com>");
+MODULE_DESCRIPTION("Amlogic Meson SAR ADC driver");
+MODULE_LICENSE("GPL v2");