iio: adc: sc27xx: Add ADC scale calibration

This patch adds support to read calibration values from the eFuse
controller to calibrate the ADC channel scales, which can make ADC
sample data more accurate.
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/adc/sprd,sc27xx-adc.txt

@@ -12,6 +12,8 @@ Required properties:
 - interrupts: The interrupt number for the ADC device.
 - #io-channel-cells: Number of cells in an IIO specifier.
 - hwlocks: Reference to a phandle of a hwlock provider node.
+- nvmem-cells: A phandle to the calibration cells provided by eFuse device.
+- nvmem-cell-names: Should be "big_scale_calib", "small_scale_calib".
 
 Example:
 
@@ -32,5 +34,7 @@ Example:
 			interrupts = <0 IRQ_TYPE_LEVEL_HIGH>;
 			#io-channel-cells = <1>;
 			hwlocks = <&hwlock 4>;
+			nvmem-cells = <&adc_big_scale>, <&adc_small_scale>;
+			nvmem-cell-names = "big_scale_calib", "small_scale_calib";
 		};
 	};

drivers/iio/adc/sc27xx_adc.c

@@ -5,10 +5,12 @@
 #include <linux/iio/iio.h>
 #include <linux/interrupt.h>
 #include <linux/module.h>
+#include <linux/nvmem-consumer.h>
 #include <linux/of.h>
 #include <linux/of_device.h>
 #include <linux/platform_device.h>
 #include <linux/regmap.h>
+#include <linux/slab.h>
 
 /* PMIC global registers definition */
 #define SC27XX_MODULE_EN		0xc08
@@ -87,16 +89,73 @@ struct sc27xx_adc_linear_graph {
  * should use the small-scale graph, and if more than 1.2v, we should use the
  * big-scale graph.
  */
-static const struct sc27xx_adc_linear_graph big_scale_graph = {
+static struct sc27xx_adc_linear_graph big_scale_graph = {
 	4200, 3310,
 	3600, 2832,
 };
 
-static const struct sc27xx_adc_linear_graph small_scale_graph = {
+static struct sc27xx_adc_linear_graph small_scale_graph = {
 	1000, 3413,
 	100, 341,
 };
 
+static const struct sc27xx_adc_linear_graph big_scale_graph_calib = {
+	4200, 856,
+	3600, 733,
+};
+
+static const struct sc27xx_adc_linear_graph small_scale_graph_calib = {
+	1000, 833,
+	100, 80,
+};
+
+static int sc27xx_adc_get_calib_data(u32 calib_data, int calib_adc)
+{
+	return ((calib_data & 0xff) + calib_adc - 128) * 4;
+}
+
+static int sc27xx_adc_scale_calibration(struct sc27xx_adc_data *data,
+					bool big_scale)
+{
+	const struct sc27xx_adc_linear_graph *calib_graph;
+	struct sc27xx_adc_linear_graph *graph;
+	struct nvmem_cell *cell;
+	const char *cell_name;
+	u32 calib_data = 0;
+	void *buf;
+	size_t len;
+
+	if (big_scale) {
+		calib_graph = &big_scale_graph_calib;
+		graph = &big_scale_graph;
+		cell_name = "big_scale_calib";
+	} else {
+		calib_graph = &small_scale_graph_calib;
+		graph = &small_scale_graph;
+		cell_name = "small_scale_calib";
+	}
+
+	cell = nvmem_cell_get(data->dev, cell_name);
+	if (IS_ERR(cell))
+		return PTR_ERR(cell);
+
+	buf = nvmem_cell_read(cell, &len);
+	nvmem_cell_put(cell);
+
+	if (IS_ERR(buf))
+		return PTR_ERR(buf);
+
+	memcpy(&calib_data, buf, min(len, sizeof(u32)));
+
+	/* Only need to calibrate the adc values in the linear graph. */
+	graph->adc0 = sc27xx_adc_get_calib_data(calib_data, calib_graph->adc0);
+	graph->adc1 = sc27xx_adc_get_calib_data(calib_data >> 8,
+						calib_graph->adc1);
+
+	kfree(buf);
+	return 0;
+}
+
 static int sc27xx_adc_get_ratio(int channel, int scale)
 {
 	switch (channel) {
@@ -209,7 +268,7 @@ static void sc27xx_adc_volt_ratio(struct sc27xx_adc_data *data,
 	*div_denominator = ratio & SC27XX_RATIO_DENOMINATOR_MASK;
 }
 
-static int sc27xx_adc_to_volt(const struct sc27xx_adc_linear_graph *graph,
+static int sc27xx_adc_to_volt(struct sc27xx_adc_linear_graph *graph,
 			      int raw_adc)
 {
 	int tmp;
@@ -390,6 +449,15 @@ static int sc27xx_adc_enable(struct sc27xx_adc_data *data)
 	if (ret)
 		goto disable_clk;
 
+	/* ADC channel scales' calibration from nvmem device */
+	ret = sc27xx_adc_scale_calibration(data, true);
+	if (ret)
+		goto disable_clk;
+
+	ret = sc27xx_adc_scale_calibration(data, false);
+	if (ret)
+		goto disable_clk;
+
 	return 0;
 
 disable_clk: