[PATCH v3 2/3] HID: i2c-hid: Retry HID descriptor read to wake up STM devices

Kenny Levinsen
2024-04-26T22:57:57Z

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 sent to them will fail on a bus error.

Retry once on bus error 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@chromium.org/#t
Co-developed-by: Radoslaw Biernacki <rad@chromium.org>
Co-developed-by: Lukasz Majczak <lma@chromium.org>
Tested-by: Lukasz Majczak <lma@chromium.org>
Reviewed-by: Lukasz Majczak <lma@chromium.org>
Signed-off-by: Kenny Levinsen <kl@kl.wtf>
---
drivers/hid/i2c-hid/i2c-hid-core.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/hid/i2c-hid/i2c-hid-core.c b/drivers/hid/i2c-hid/i2c-hid-core.c
index 6ffa43d245b4..6ac1b11fb675 100644
--- a/drivers/hid/i2c-hid/i2c-hid-core.c
+++ b/drivers/hid/i2c-hid/i2c-hid-core.c
@@ -991,8 +991,17 @@ 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 on a bus error. Retry the command in this case.
+ */
ret = i2c_hid_fetch_hid_descriptor(ihid);
- if (ret < 0) {
+ if (ret == -ENXIO) {
+ usleep_range(400, 500);
+ ret = i2c_hid_fetch_hid_descriptor(ihid);
+ }
+ if (ret) {
i2c_hid_dbg(ihid, "failed to fetch HID descriptor: %d\n", ret);
return ret;
}
--
2.44.0