[PATCH v3 5/5] at24: Support probing while off

[Sakari Ailus <sakari.ailus@linux.intel.com>]

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@linux.intel.com>
---
 drivers/misc/eeprom/at24.c | 31 +++++++++++++++++++++----------
 1 file changed, 21 insertions(+), 10 deletions(-)

diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
index 0681d5fdd538a..41ac65d1e5d41 100644
--- a/drivers/misc/eeprom/at24.c
+++ b/drivers/misc/eeprom/at24.c
@@ -564,6 +564,7 @@ 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;
@@ -701,19 +702,24 @@ static int at24_probe(struct i2c_client *client)
 
 	i2c_set_clientdata(client, at24);
 
-	/* enable runtime pm */
-	pm_runtime_set_active(dev);
+	low_power = acpi_dev_low_power_state_probe(&client->dev);
+	if (!low_power)
+		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);
-	pm_runtime_idle(dev);
-	if (err) {
-		pm_runtime_disable(dev);
-		return -ENODEV;
+	if (!low_power) {
+		err = at24_read(at24, 0, &test_byte, 1);
+		pm_runtime_idle(dev);
+		if (err) {
+			pm_runtime_disable(dev);
+			return -ENODEV;
+		}
 	}
 
 	if (writable)
@@ -728,8 +734,12 @@ static int at24_probe(struct i2c_client *client)
 
 static int at24_remove(struct i2c_client *client)
 {
+	bool low_power;
+
 	pm_runtime_disable(&client->dev);
-	pm_runtime_set_suspended(&client->dev);
+	low_power = acpi_dev_low_power_state_probe(&client->dev);
+	if (!low_power)
+		pm_runtime_set_suspended(&client->dev);
 
 	return 0;
 }
@@ -743,6 +753,7 @@ static struct i2c_driver at24_driver = {
 	.probe_new = at24_probe,
 	.remove = at24_remove,
 	.id_table = at24_ids,
+	.probe_low_power = true,
 };
 
 static int __init at24_init(void)
-- 
2.20.1