ACPI / PMIC: xpower: Fix TS-pin current-source handling

The current-source used for the battery temp-sensor (TS) is shared with the
GPADC. For proper fuel-gauge and charger operation the TS current-source
needs to be permanently on. But to read the GPADC we need to temporary
switch the TS current-source to ondemand, so that the GPADC can use it,
otherwise we will always read an all 0 value.

The switching from on to on-ondemand is not necessary when the TS
current-source is off (this happens on devices which do not have a TS).

Prior to this commit there were 2 issues with our handling of the TS
current-source switching:

 1) We were writing hardcoded values to the ADC TS pin-ctrl register,
 overwriting various other unrelated bits. Specifically we were overwriting
 the current-source setting for the TS and GPIO0 pins, forcing it to 80ųA
 independent of its original setting. On a Chuwi Vi10 tablet this was
 causing us to get a too high adc value (due to a too high current-source)
 resulting in acpi_lpat_raw_to_temp() returning -ENOENT, resulting in:

ACPI Error: AE_ERROR, Returned by Handler for [UserDefinedRegion]
ACPI Error: Method parse/execution failed \_SB.SXP1._TMP, AE_ERROR

This commit fixes this by using regmap_update_bits to change only the
relevant bits.

 2) At the end of intel_xpower_pmic_get_raw_temp() we were unconditionally
 enabling the TS current-source even on devices where the TS-pin is not used
 and the current-source thus was off on entry of the function.

This commit fixes this by checking if the TS current-source is off when
entering intel_xpower_pmic_get_raw_temp() and if so it is left as is.

Fixes: 58eefe2f (ACPI / PMIC: xpower: Do pinswitch ... reading GPADC)
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: 4.14+ <stable@vger.kernel.org> # 4.14+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/pmic/intel_pmic_xpower.c

@@ -20,8 +20,11 @@
 #define GPI1_LDO_ON		(3 << 0)
 #define GPI1_LDO_OFF		(4 << 0)
 
-#define AXP288_ADC_TS_PIN_GPADC	0xf2
-#define AXP288_ADC_TS_PIN_ON	0xf3
+#define AXP288_ADC_TS_CURRENT_ON_OFF_MASK		GENMASK(1, 0)
+#define AXP288_ADC_TS_CURRENT_OFF			(0 << 0)
+#define AXP288_ADC_TS_CURRENT_ON_WHEN_CHARGING		(1 << 0)
+#define AXP288_ADC_TS_CURRENT_ON_ONDEMAND		(2 << 0)
+#define AXP288_ADC_TS_CURRENT_ON			(3 << 0)
 
 static struct pmic_table power_table[] = {
 	{
@@ -212,22 +215,44 @@ static int intel_xpower_pmic_update_power(struct regmap *regmap, int reg,
  */
 static int intel_xpower_pmic_get_raw_temp(struct regmap *regmap, int reg)
 {
+	int ret, adc_ts_pin_ctrl;
 	u8 buf[2];
-	int ret;
 
-	ret = regmap_write(regmap, AXP288_ADC_TS_PIN_CTRL,
-			   AXP288_ADC_TS_PIN_GPADC);
+	/*
+	 * The current-source used for the battery temp-sensor (TS) is shared
+	 * with the GPADC. For proper fuel-gauge and charger operation the TS
+	 * current-source needs to be permanently on. But to read the GPADC we
+	 * need to temporary switch the TS current-source to ondemand, so that
+	 * the GPADC can use it, otherwise we will always read an all 0 value.
+	 *
+	 * Note that the switching from on to on-ondemand is not necessary
+	 * when the TS current-source is off (this happens on devices which
+	 * do not use the TS-pin).
+	 */
+	ret = regmap_read(regmap, AXP288_ADC_TS_PIN_CTRL, &adc_ts_pin_ctrl);
 	if (ret)
 		return ret;
 
-	/* After switching to the GPADC pin give things some time to settle */
+	if (adc_ts_pin_ctrl & AXP288_ADC_TS_CURRENT_ON_OFF_MASK) {
+		ret = regmap_update_bits(regmap, AXP288_ADC_TS_PIN_CTRL,
+					 AXP288_ADC_TS_CURRENT_ON_OFF_MASK,
+					 AXP288_ADC_TS_CURRENT_ON_ONDEMAND);
+		if (ret)
+			return ret;
+
+		/* Wait a bit after switching the current-source */
 		usleep_range(6000, 10000);
+	}
 
 	ret = regmap_bulk_read(regmap, AXP288_GP_ADC_H, buf, 2);
 	if (ret == 0)
 		ret = (buf[0] << 4) + ((buf[1] >> 4) & 0x0f);
 
-	regmap_write(regmap, AXP288_ADC_TS_PIN_CTRL, AXP288_ADC_TS_PIN_ON);
+	if (adc_ts_pin_ctrl & AXP288_ADC_TS_CURRENT_ON_OFF_MASK) {
+		regmap_update_bits(regmap, AXP288_ADC_TS_PIN_CTRL,
+				   AXP288_ADC_TS_CURRENT_ON_OFF_MASK,
+				   AXP288_ADC_TS_CURRENT_ON);
+	}
 
 	return ret;
 }