[PATCH v4 06/11] iio: light: cm32181: Handle CM3218 ACPI devices with 2 I2C resources

[Hans de Goede <hdegoede@redhat.com>]

Some ACPI systems list 2 I2C resources for the CM3218 sensor. On these
systems the first I2cSerialBus ACPI-resource points to the SMBus Alert
Response Address (ARA, 0x0c) and the second I2cSerialBus ACPI-resource
points to the actual CM3218 sensor address:

 Method (_CRS, 0, NotSerialized)  // _CRS: Current Resource Settings
 {
     Name (SBUF, ResourceTemplate ()
     {
         I2cSerialBusV2 (0x000C, ControllerInitiated, 0x00061A80,
             AddressingMode7Bit, "\\_SB.I2C3",
             0x00, ResourceConsumer, , Exclusive,
             )
         I2cSerialBusV2 (0x0048, ControllerInitiated, 0x00061A80,
             AddressingMode7Bit, "\\_SB.I2C3",
             0x00, ResourceConsumer, , Exclusive,
             )
         Interrupt (ResourceConsumer, Level, ActiveHigh, Exclusive, ,, )
         {
             0x00000033,
         }
     })
     Return (SBUF) /* \_SB_.I2C3.ALSD._CRS.SBUF */
 }

Detect this and take the following step to deal with it:

1. When a SMBus Alert capable sensor has an Alert asserted, it will
   not respond on its actual I2C address. Read a byte from the ARA
   to clear any pending Alerts.

2. Create a "dummy" client for the actual I2C address and
   use that client to communicate with the sensor.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
Changes in v3:
- Create and use a dummy client instead of relying on i2c-multi-instantiate
  to create 2 separate clients for the 2 I2C resources

Changes in v2
- s/i2c_client-s/I2C clients/ in added comment
---
 drivers/iio/light/cm32181.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/drivers/iio/light/cm32181.c b/drivers/iio/light/cm32181.c
index f6261798baa3..fd760e209dfa 100644
--- a/drivers/iio/light/cm32181.c
+++ b/drivers/iio/light/cm32181.c
@@ -51,6 +51,8 @@
 #define CM32181_CALIBSCALE_RESOLUTION	1000
 #define MLUX_PER_LUX			1000
 
+#define SMBUS_ALERT_RESPONSE_ADDRESS	0x0c
+
 static const u8 cm32181_reg[CM32181_CONF_REG_NUM] = {
 	CM32181_REG_ADDR_CMD,
 };
@@ -351,6 +353,26 @@ static int cm32181_probe(struct i2c_client *client)
 	if (!indio_dev)
 		return -ENOMEM;
 
+	/*
+	 * Some ACPI systems list 2 I2C resources for the CM3218 sensor, the
+	 * SMBus Alert Response Address (ARA, 0x0c) and the actual I2C address.
+	 * Detect this and take the following step to deal with it:
+	 * 1. When a SMBus Alert capable sensor has an Alert asserted, it will
+	 *    not respond on its actual I2C address. Read a byte from the ARA
+	 *    to clear any pending Alerts.
+	 * 2. Create a "dummy" client for the actual I2C address and
+	 *    use that client to communicate with the sensor.
+	 */
+	if (ACPI_HANDLE(dev) && client->addr == SMBUS_ALERT_RESPONSE_ADDRESS) {
+		struct i2c_board_info board_info = { .type = "dummy" };
+
+		i2c_smbus_read_byte(client);
+
+		client = i2c_acpi_new_device(dev, 1, &board_info);
+		if (IS_ERR(client))
+			return PTR_ERR(client);
+	}
+
 	cm32181 = iio_priv(indio_dev);
 	cm32181->client = client;
 
-- 
2.26.0