[PATCH v5 5/6] at24: Support probing while off

[Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>]

In certain use cases (where the chip is part of a camera module, and the
camera module is wired together with a camera privacy LED), powering on
the device during probe is undesirable. Add support for the at24 to
execute probe while being powered off. For this to happen, a hint in form
of a device property is required from the firmware.

Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
---
 drivers/misc/eeprom/at24.c | 40 ++++++++++++++++++++++++--------------
 1 file changed, 25 insertions(+), 15 deletions(-)

diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
index 2591c21b2b5d8..e597a8861e817 100644
--- a/drivers/misc/eeprom/at24.c
+++ b/drivers/misc/eeprom/at24.c
@@ -561,6 +561,7 @@ static int at24_probe(struct i2c_client *client)
 	bool i2c_fn_i2c, i2c_fn_block;
 	unsigned int i, num_addresses;
 	struct at24_data *at24;
+	bool low_power;
 	struct regmap *regmap;
 	bool writable;
 	u8 test_byte;
@@ -698,25 +699,30 @@ static int at24_probe(struct i2c_client *client)
 
 	i2c_set_clientdata(client, at24);
 
-	err = regulator_enable(at24->vcc_reg);
-	if (err) {
-		dev_err(dev, "Failed to enable vcc regulator\n");
-		return err;
-	}
+	low_power = acpi_dev_state_low_power(&client->dev);
+	if (!low_power) {
+		err = regulator_enable(at24->vcc_reg);
+		if (err) {
+			dev_err(dev, "Failed to enable vcc regulator\n");
+			return err;
+		}
 
-	/* enable runtime pm */
-	pm_runtime_set_active(dev);
+		pm_runtime_set_active(dev);
+	}
 	pm_runtime_enable(dev);
 
 	/*
-	 * Perform a one-byte test read to verify that the
-	 * chip is functional.
+	 * Perform a one-byte test read to verify that the chip is functional,
+	 * unless powering on the device is to be avoided during probe (i.e.
+	 * it's powered off right now).
 	 */
-	err = at24_read(at24, 0, &test_byte, 1);
-	if (err) {
-		pm_runtime_disable(dev);
-		regulator_disable(at24->vcc_reg);
-		return -ENODEV;
+	if (!low_power) {
+		err = at24_read(at24, 0, &test_byte, 1);
+		if (err) {
+			pm_runtime_disable(dev);
+			regulator_disable(at24->vcc_reg);
+			return -ENODEV;
+		}
 	}
 
 	pm_runtime_idle(dev);
@@ -734,11 +740,14 @@ static int at24_probe(struct i2c_client *client)
 static int at24_remove(struct i2c_client *client)
 {
 	struct at24_data *at24 = i2c_get_clientdata(client);
+	bool low_power;
 
 	pm_runtime_disable(&client->dev);
 	if (!pm_runtime_status_suspended(&client->dev))
 		regulator_disable(at24->vcc_reg);
-	pm_runtime_set_suspended(&client->dev);
+	low_power = acpi_dev_state_low_power(&client->dev);
+	if (!low_power)
+		pm_runtime_set_suspended(&client->dev);
 
 	return 0;
 }
@@ -775,6 +784,7 @@ static struct i2c_driver at24_driver = {
 	.probe_new = at24_probe,
 	.remove = at24_remove,
 	.id_table = at24_ids,
+	.flags = I2C_DRV_FL_ALLOW_LOW_POWER_PROBE,
 };
 
 static int __init at24_init(void)
-- 
2.20.1