ACPI / PMIC: XPower: optimize I2C-bus accesses

The I2C-bus to the XPower AXP288 is shared between the Linux kernel and
the SoCs P-Unit. The P-Unit has a semaphore which the kernel must "lock"
before it may use the bus and while the kernel holds the semaphore the CPU
and GPU power-states must not be changed otherwise the system will freeze.

This is a complex process, which is quite expensive. This is all done by
iosf_mbi_block_punit_i2c_access(). To ensure that no unguarded I2C-bus
accesses happen, iosf_mbi_block_punit_i2c_access() gets called by the
I2C-bus-driver for every I2C transfer. Because this is so expensive it
is allowed to call iosf_mbi_block_punit_i2c_access() in a nested
fashion, so that higher-level code which does multiple I2C-transfers can
call it once for a group of transfers, turning the calls done by the
I2C-bus-driver into no-ops.

Add iosf_mbi_block_punit_i2c_access() calls around groups of register
accesses, so that the P-Unit semaphore only needs to be taken once
for each group of register accesses.

Reviewed-by: Andy Shevchenko <[email protected]>
Signed-off-by: Hans de Goede <[email protected]>
Signed-off-by: Rafael J. Wysocki <[email protected]>

Author: jwrdegoede

drivers/acpi/pmic/intel_pmic_xpower.c

@@ -178,15 +178,17 @@ static int intel_xpower_pmic_update_power(struct regmap *regmap, int reg,
 {
 	int data, ret;
 
-	/* GPIO1 LDO regulator needs special handling */
-	if (reg == XPOWER_GPI1_CTRL)
-		return regmap_update_bits(regmap, reg, GPI1_LDO_MASK,
-					  on ? GPI1_LDO_ON : GPI1_LDO_OFF);
-
 	ret = iosf_mbi_block_punit_i2c_access();
 	if (ret)
 		return ret;
 
+	/* GPIO1 LDO regulator needs special handling */
+	if (reg == XPOWER_GPI1_CTRL) {
+		ret = regmap_update_bits(regmap, reg, GPI1_LDO_MASK,
+					 on ? GPI1_LDO_ON : GPI1_LDO_OFF);
+		goto out;
+	}
+
 	if (regmap_read(regmap, reg, &data)) {
 		ret = -EIO;
 		goto out;
@@ -234,6 +236,11 @@ static int intel_xpower_pmic_get_raw_temp(struct regmap *regmap, int reg)
 		return ret;
 
 	if (adc_ts_pin_ctrl & AXP288_ADC_TS_CURRENT_ON_OFF_MASK) {
+		/*
+		 * AXP288_ADC_TS_PIN_CTRL reads are cached by the regmap, so
+		 * this does to a single I2C-transfer, and thus there is no
+		 * need to explicitly call iosf_mbi_block_punit_i2c_access().
+		 */
 		ret = regmap_update_bits(regmap, AXP288_ADC_TS_PIN_CTRL,
 					 AXP288_ADC_TS_CURRENT_ON_OFF_MASK,
 					 AXP288_ADC_TS_CURRENT_ON_ONDEMAND);
@@ -244,6 +251,10 @@ static int intel_xpower_pmic_get_raw_temp(struct regmap *regmap, int reg)
 		usleep_range(6000, 10000);
 	}
 
+	ret = iosf_mbi_block_punit_i2c_access();
+	if (ret)
+		return ret;
+
 	ret = regmap_bulk_read(regmap, AXP288_GP_ADC_H, buf, 2);
 	if (ret == 0)
 		ret = (buf[0] << 4) + ((buf[1] >> 4) & 0x0f);
@@ -254,6 +265,8 @@ static int intel_xpower_pmic_get_raw_temp(struct regmap *regmap, int reg)
 				   AXP288_ADC_TS_CURRENT_ON);
 	}
 
+	iosf_mbi_unblock_punit_i2c_access();
+
 	return ret;
 }