mfd: Calibrate ab8500 gpadc using OTP values

The GPADC found in the AB8500 needs to be calibrated to work
properly. This is done by writing a number of special OTP
(one-time-programmable) registers at production. This patch
makes sure that these values are used to calibrate the returned
value from the GPADC so that it is correct.

Signed-off-by: Johan Palsson <johan.palsson@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

drivers/mfd/ab8500-gpadc.c

@@ -4,6 +4,7 @@
  * License Terms: GNU General Public License v2
  * Author: Arun R Murthy <arun.murthy@stericsson.com>
  * Author: Daniel Willerud <daniel.willerud@stericsson.com>
+ * Author: Johan Palsson <johan.palsson@stericsson.com>
  */
 #include <linux/init.h>
 #include <linux/module.h>
@@ -36,6 +37,18 @@
 #define AB8500_GPADC_AUTODATAH_REG	0x08
 #define AB8500_GPADC_MUX_CTRL_REG	0x09
 
+/*
+ * OTP register offsets
+ * Bank : 0x15
+ */
+#define AB8500_GPADC_CAL_1		0x0F
+#define AB8500_GPADC_CAL_2		0x10
+#define AB8500_GPADC_CAL_3		0x11
+#define AB8500_GPADC_CAL_4		0x12
+#define AB8500_GPADC_CAL_5		0x13
+#define AB8500_GPADC_CAL_6		0x14
+#define AB8500_GPADC_CAL_7		0x15
+
 /* gpadc constants */
 #define EN_VINTCORE12			0x04
 #define EN_VTVOUT			0x02
@@ -47,8 +60,46 @@
 #define DIS_ZERO			0x00
 #define GPADC_BUSY			0x01
 
+/* GPADC constants from AB8500 spec, UM0836 */
+#define ADC_RESOLUTION			1024
+#define ADC_CH_BTEMP_MIN		0
+#define ADC_CH_BTEMP_MAX		1350
+#define ADC_CH_DIETEMP_MIN		0
+#define ADC_CH_DIETEMP_MAX		1350
+#define ADC_CH_CHG_V_MIN		0
+#define ADC_CH_CHG_V_MAX		20030
+#define ADC_CH_ACCDET2_MIN		0
+#define ADC_CH_ACCDET2_MAX		2500
+#define ADC_CH_VBAT_MIN			2300
+#define ADC_CH_VBAT_MAX			4800
+#define ADC_CH_CHG_I_MIN		0
+#define ADC_CH_CHG_I_MAX		1500
+#define ADC_CH_BKBAT_MIN		0
+#define ADC_CH_BKBAT_MAX		3200
+
+/* This is used to not lose precision when dividing to get gain and offset */
+#define CALIB_SCALE			1000
+
+enum cal_channels {
+	ADC_INPUT_VMAIN = 0,
+	ADC_INPUT_BTEMP,
+	ADC_INPUT_VBAT,
+	NBR_CAL_INPUTS,
+};
+
+/**
+ * struct adc_cal_data - Table for storing gain and offset for the calibrated
+ * ADC channels
+ * @gain:		Gain of the ADC channel
+ * @offset:		Offset of the ADC channel
+ */
+struct adc_cal_data {
+	u64 gain;
+	u64 offset;
+};
+
 /**
- * struct ab8500_gpadc - ab8500 GPADC device information
+ * struct ab8500_gpadc - AB8500 GPADC device information
  * @dev:			pointer to the struct device
  * @node:			a list of AB8500 GPADCs, hence prepared for
 				reentrance
@@ -57,6 +108,7 @@
  * @ab8500_gpadc_lock:		structure of type mutex
  * @regu:			pointer to the struct regulator
  * @irq:			interrupt number that is used by gpadc
+ * @cal_data			array of ADC calibration data structs
  */
 struct ab8500_gpadc {
 	struct device *dev;
@@ -65,6 +117,7 @@ struct ab8500_gpadc {
 	struct mutex ab8500_gpadc_lock;
 	struct regulator *regu;
 	int irq;
+	struct adc_cal_data cal_data[NBR_CAL_INPUTS];
 };
 
 static LIST_HEAD(ab8500_gpadc_list);
@@ -86,13 +139,102 @@ struct ab8500_gpadc *ab8500_gpadc_get(char *name)
 }
 EXPORT_SYMBOL(ab8500_gpadc_get);
 
+static int ab8500_gpadc_ad_to_voltage(struct ab8500_gpadc *gpadc, u8 input,
+	int ad_value)
+{
+	int res;
+
+	switch (input) {
+	case MAIN_CHARGER_V:
+		/* For some reason we don't have calibrated data */
+		if (!gpadc->cal_data[ADC_INPUT_VMAIN].gain) {
+			res = ADC_CH_CHG_V_MIN + (ADC_CH_CHG_V_MAX -
+				ADC_CH_CHG_V_MIN) * ad_value /
+				ADC_RESOLUTION;
+			break;
+		}
+		/* Here we can use the calibrated data */
+		res = (int) (ad_value * gpadc->cal_data[ADC_INPUT_VMAIN].gain +
+			gpadc->cal_data[ADC_INPUT_VMAIN].offset) / CALIB_SCALE;
+		break;
+
+	case BAT_CTRL:
+	case BTEMP_BALL:
+	case ACC_DETECT1:
+	case ADC_AUX1:
+	case ADC_AUX2:
+		/* For some reason we don't have calibrated data */
+		if (!gpadc->cal_data[ADC_INPUT_BTEMP].gain) {
+			res = ADC_CH_BTEMP_MIN + (ADC_CH_BTEMP_MAX -
+				ADC_CH_BTEMP_MIN) * ad_value /
+				ADC_RESOLUTION;
+			break;
+		}
+		/* Here we can use the calibrated data */
+		res = (int) (ad_value * gpadc->cal_data[ADC_INPUT_BTEMP].gain +
+			gpadc->cal_data[ADC_INPUT_BTEMP].offset) / CALIB_SCALE;
+		break;
+
+	case MAIN_BAT_V:
+		/* For some reason we don't have calibrated data */
+		if (!gpadc->cal_data[ADC_INPUT_VBAT].gain) {
+			res = ADC_CH_VBAT_MIN + (ADC_CH_VBAT_MAX -
+				ADC_CH_VBAT_MIN) * ad_value /
+				ADC_RESOLUTION;
+			break;
+		}
+		/* Here we can use the calibrated data */
+		res = (int) (ad_value * gpadc->cal_data[ADC_INPUT_VBAT].gain +
+			gpadc->cal_data[ADC_INPUT_VBAT].offset) / CALIB_SCALE;
+		break;
+
+	case DIE_TEMP:
+		res = ADC_CH_DIETEMP_MIN +
+			(ADC_CH_DIETEMP_MAX - ADC_CH_DIETEMP_MIN) * ad_value /
+			ADC_RESOLUTION;
+		break;
+
+	case ACC_DETECT2:
+		res = ADC_CH_ACCDET2_MIN +
+			(ADC_CH_ACCDET2_MAX - ADC_CH_ACCDET2_MIN) * ad_value /
+			ADC_RESOLUTION;
+		break;
+
+	case VBUS_V:
+		res = ADC_CH_CHG_V_MIN +
+			(ADC_CH_CHG_V_MAX - ADC_CH_CHG_V_MIN) * ad_value /
+			ADC_RESOLUTION;
+		break;
+
+	case MAIN_CHARGER_C:
+	case USB_CHARGER_C:
+		res = ADC_CH_CHG_I_MIN +
+			(ADC_CH_CHG_I_MAX - ADC_CH_CHG_I_MIN) * ad_value /
+			ADC_RESOLUTION;
+		break;
+
+	case BK_BAT_V:
+		res = ADC_CH_BKBAT_MIN +
+			(ADC_CH_BKBAT_MAX - ADC_CH_BKBAT_MIN) * ad_value /
+			ADC_RESOLUTION;
+		break;
+
+	default:
+		dev_err(gpadc->dev,
+			"unknown channel, not possible to convert\n");
+		res = -EINVAL;
+		break;
+
+	}
+	return res;
+}
+
 /**
  * ab8500_gpadc_convert() - gpadc conversion
  * @input:	analog input to be converted to digital data
  *
  * This function converts the selected analog i/p to digital
- * data. Thereafter calibration has to be made to obtain the
- * data in the required quantity measurement.
+ * data.
  */
 int ab8500_gpadc_convert(struct ab8500_gpadc *gpadc, u8 input)
 {
@@ -189,7 +331,8 @@ int ab8500_gpadc_convert(struct ab8500_gpadc *gpadc, u8 input)
 	/* Disable VTVout LDO this is required for GPADC */
 	regulator_disable(gpadc->regu);
 	mutex_unlock(&gpadc->ab8500_gpadc_lock);
-	return data;
+	ret = ab8500_gpadc_ad_to_voltage(gpadc, input, data);
+	return ret;
 
 out:
 	/*
@@ -227,6 +370,138 @@ static irqreturn_t ab8500_bm_gpswadcconvend_handler(int irq, void *_gpadc)
 	return IRQ_HANDLED;
 }
 
+static int otp_cal_regs[] = {
+	AB8500_GPADC_CAL_1,
+	AB8500_GPADC_CAL_2,
+	AB8500_GPADC_CAL_3,
+	AB8500_GPADC_CAL_4,
+	AB8500_GPADC_CAL_5,
+	AB8500_GPADC_CAL_6,
+	AB8500_GPADC_CAL_7,
+};
+
+static void ab8500_gpadc_read_calibration_data(struct ab8500_gpadc *gpadc)
+{
+	int i;
+	int ret[ARRAY_SIZE(otp_cal_regs)];
+	u8 gpadc_cal[ARRAY_SIZE(otp_cal_regs)];
+
+	int vmain_high, vmain_low;
+	int btemp_high, btemp_low;
+	int vbat_high, vbat_low;
+
+	/* First we read all OTP registers and store the error code */
+	for (i = 0; i < ARRAY_SIZE(otp_cal_regs); i++) {
+		ret[i] = abx500_get_register_interruptible(gpadc->dev,
+			AB8500_OTP_EMUL, otp_cal_regs[i],  &gpadc_cal[i]);
+		if (ret[i] < 0)
+			dev_err(gpadc->dev, "%s: read otp reg 0x%02x failed\n",
+				__func__, otp_cal_regs[i]);
+	}
+
+	/*
+	 * The ADC calibration data is stored in OTP registers.
+	 * The layout of the calibration data is outlined below and a more
+	 * detailed description can be found in UM0836
+	 *
+	 * vm_h/l = vmain_high/low
+	 * bt_h/l = btemp_high/low
+	 * vb_h/l = vbat_high/low
+	 *
+	 * Data bits:
+	 * | 7	   | 6	   | 5	   | 4	   | 3	   | 2	   | 1	   | 0
+	 * |.......|.......|.......|.......|.......|.......|.......|.......
+	 * |						   | vm_h9 | vm_h8
+	 * |.......|.......|.......|.......|.......|.......|.......|.......
+	 * |		   | vm_h7 | vm_h6 | vm_h5 | vm_h4 | vm_h3 | vm_h2
+	 * |.......|.......|.......|.......|.......|.......|.......|.......
+	 * | vm_h1 | vm_h0 | vm_l4 | vm_l3 | vm_l2 | vm_l1 | vm_l0 | bt_h9
+	 * |.......|.......|.......|.......|.......|.......|.......|.......
+	 * | bt_h8 | bt_h7 | bt_h6 | bt_h5 | bt_h4 | bt_h3 | bt_h2 | bt_h1
+	 * |.......|.......|.......|.......|.......|.......|.......|.......
+	 * | bt_h0 | bt_l4 | bt_l3 | bt_l2 | bt_l1 | bt_l0 | vb_h9 | vb_h8
+	 * |.......|.......|.......|.......|.......|.......|.......|.......
+	 * | vb_h7 | vb_h6 | vb_h5 | vb_h4 | vb_h3 | vb_h2 | vb_h1 | vb_h0
+	 * |.......|.......|.......|.......|.......|.......|.......|.......
+	 * | vb_l5 | vb_l4 | vb_l3 | vb_l2 | vb_l1 | vb_l0 |
+	 * |.......|.......|.......|.......|.......|.......|.......|.......
+	 *
+	 *
+	 * Ideal output ADC codes corresponding to injected input voltages
+	 * during manufacturing is:
+	 *
+	 * vmain_high: Vin = 19500mV / ADC ideal code = 997
+	 * vmain_low:  Vin = 315mV   / ADC ideal code = 16
+	 * btemp_high: Vin = 1300mV  / ADC ideal code = 985
+	 * btemp_low:  Vin = 21mV    / ADC ideal code = 16
+	 * vbat_high:  Vin = 4700mV  / ADC ideal code = 982
+	 * vbat_low:   Vin = 2380mV  / ADC ideal code = 33
+	 */
+
+	/* Calculate gain and offset for VMAIN if all reads succeeded */
+	if (!(ret[0] < 0 || ret[1] < 0 || ret[2] < 0)) {
+		vmain_high = (((gpadc_cal[0] & 0x03) << 8) |
+			((gpadc_cal[1] & 0x3F) << 2) |
+			((gpadc_cal[2] & 0xC0) >> 6));
+
+		vmain_low = ((gpadc_cal[2] & 0x3E) >> 1);
+
+		gpadc->cal_data[ADC_INPUT_VMAIN].gain = CALIB_SCALE *
+			(19500 - 315) /	(vmain_high - vmain_low);
+
+		gpadc->cal_data[ADC_INPUT_VMAIN].offset = CALIB_SCALE * 19500 -
+			(CALIB_SCALE * (19500 - 315) /
+			 (vmain_high - vmain_low)) * vmain_high;
+	} else {
+		gpadc->cal_data[ADC_INPUT_VMAIN].gain = 0;
+	}
+
+	/* Calculate gain and offset for BTEMP if all reads succeeded */
+	if (!(ret[2] < 0 || ret[3] < 0 || ret[4] < 0)) {
+		btemp_high = (((gpadc_cal[2] & 0x01) << 9) |
+			(gpadc_cal[3] << 1) |
+			((gpadc_cal[4] & 0x80) >> 7));
+
+		btemp_low = ((gpadc_cal[4] & 0x7C) >> 2);
+
+		gpadc->cal_data[ADC_INPUT_BTEMP].gain =
+			CALIB_SCALE * (1300 - 21) / (btemp_high - btemp_low);
+
+		gpadc->cal_data[ADC_INPUT_BTEMP].offset = CALIB_SCALE * 1300 -
+			(CALIB_SCALE * (1300 - 21) /
+			(btemp_high - btemp_low)) * btemp_high;
+	} else {
+		gpadc->cal_data[ADC_INPUT_BTEMP].gain = 0;
+	}
+
+	/* Calculate gain and offset for VBAT if all reads succeeded */
+	if (!(ret[4] < 0 || ret[5] < 0 || ret[6] < 0)) {
+		vbat_high = (((gpadc_cal[4] & 0x03) << 8) | gpadc_cal[5]);
+		vbat_low = ((gpadc_cal[6] & 0xFC) >> 2);
+
+		gpadc->cal_data[ADC_INPUT_VBAT].gain = CALIB_SCALE *
+			(4700 - 2380) /	(vbat_high - vbat_low);
+
+		gpadc->cal_data[ADC_INPUT_VBAT].offset = CALIB_SCALE * 4700 -
+			(CALIB_SCALE * (4700 - 2380) /
+			(vbat_high - vbat_low)) * vbat_high;
+	} else {
+		gpadc->cal_data[ADC_INPUT_VBAT].gain = 0;
+	}
+
+	dev_dbg(gpadc->dev, "VMAIN gain %llu offset %llu\n",
+		gpadc->cal_data[ADC_INPUT_VMAIN].gain,
+		gpadc->cal_data[ADC_INPUT_VMAIN].offset);
+
+	dev_dbg(gpadc->dev, "BTEMP gain %llu offset %llu\n",
+		gpadc->cal_data[ADC_INPUT_BTEMP].gain,
+		gpadc->cal_data[ADC_INPUT_BTEMP].offset);
+
+	dev_dbg(gpadc->dev, "VBAT gain %llu offset %llu\n",
+		gpadc->cal_data[ADC_INPUT_VBAT].gain,
+		gpadc->cal_data[ADC_INPUT_VBAT].offset);
+}
+
 static int __devinit ab8500_gpadc_probe(struct platform_device *pdev)
 {
 	int ret = 0;
@@ -269,6 +544,7 @@ static int __devinit ab8500_gpadc_probe(struct platform_device *pdev)
 		dev_err(gpadc->dev, "failed to get vtvout LDO\n");
 		goto fail_irq;
 	}
+	ab8500_gpadc_read_calibration_data(gpadc);
 	list_add_tail(&gpadc->node, &ab8500_gpadc_list);
 	dev_dbg(gpadc->dev, "probe success\n");
 	return 0;
@@ -318,6 +594,6 @@ subsys_initcall_sync(ab8500_gpadc_init);
 module_exit(ab8500_gpadc_exit);
 
 MODULE_LICENSE("GPL v2");
-MODULE_AUTHOR("Arun R Murthy, Daniel Willerud");
+MODULE_AUTHOR("Arun R Murthy, Daniel Willerud, Johan Palsson");
 MODULE_ALIAS("platform:ab8500_gpadc");
 MODULE_DESCRIPTION("AB8500 GPADC driver");