[RFC 1/3] imx258: Defer probing on ident register read fail (on ACPI)

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

Return -EPROBE_DEFER if probing the device fails because of the I²C
transaction (-EIO only). This generally happens when the power on sequence
of the device has not been fully performed yet due to later probing of
other drivers.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
---
 drivers/media/i2c/imx258.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/media/i2c/imx258.c b/drivers/media/i2c/imx258.c
index c249507aa2db..2751c12b6029 100644
--- a/drivers/media/i2c/imx258.c
+++ b/drivers/media/i2c/imx258.c
@@ -1109,6 +1109,14 @@ static int imx258_identify_module(struct imx258 *imx258)
 
 	ret = imx258_read_reg(imx258, IMX258_REG_CHIP_ID,
 			      IMX258_REG_VALUE_16BIT, &val);
+	if (ret == -EIO && is_acpi_device_node(dev_fwnode(&client->dev))) {
+		/*
+		 * If we get -EIO here and it's an ACPI device, there's a fair
+		 * likelihood it's because the drivers required to power this
+		 * device on have not probed yet. Thus return -EPROBE_DEFER.
+		 */
+		return -EPROBE_DEFER;
+	}
 	if (ret) {
 		dev_err(&client->dev, "failed to read chip id %x\n",
 			IMX258_CHIP_ID);
-- 
2.30.2