[PATCH v2 2/3] HID: i2c-hid: Retry HID descriptor read to wake up STM devices

[Kenny Levinsen]

Some STM microcontrollers need 400µs after rising clock edge in order to
come out of their deep sleep state. This in turn means that the first
command send to them timeout and fail with EREMOTEIO.

Retry once on EREMOTEIO to see if the device came alive, otherwise treat
the error as if no device was present like before.

Link: https://lore.kernel.org/all/20240405102436.3479210-1-lma@xxxxxxxxxxxx/#t
Co-developed-by: Radoslaw Biernacki <rad@xxxxxxxxxxxx>
Co-developed-by: Lukasz Majczak <lma@xxxxxxxxxxxx>
Signed-off-by: Kenny Levinsen <kl@xxxxxx>
---
 drivers/hid/i2c-hid/i2c-hid-core.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/hid/i2c-hid/i2c-hid-core.c b/drivers/hid/i2c-hid/i2c-hid-core.c
index 515a80dbf6c7..252ccb3b71d1 100644
--- a/drivers/hid/i2c-hid/i2c-hid-core.c
+++ b/drivers/hid/i2c-hid/i2c-hid-core.c
@@ -1010,7 +1010,17 @@ static int __i2c_hid_core_probe(struct i2c_hid *ihid)
 	struct hid_device *hid = ihid->hid;
 	int ret;
 
+	/*
+	 * Some STM-based devices need 400µs after a rising clock edge to wake
+	 * from deep sleep, which in turn means that our first command will
+	 * fail EREMOTEIO. Retry the command in this case.
+	 */
 	ret = i2c_hid_fetch_hid_descriptor(ihid);
+	if (ret == -EREMOTEIO) {
+		usleep_range(400, 500);
+		ret = i2c_hid_fetch_hid_descriptor(ihid);
+	}
+
 	if (ret == -EREMOTEIO) {
 		i2c_hid_dbg(ihid, "nothing at this address: %d\n", ret);
 		return -ENXIO;
-- 
2.44.0