[PATCH v2] HID: i2c-hid: wait for i2c touchpad deep-sleep to power-up transition

[Lukasz Majczak]

This patch extends the early bailout for probing procedure introduced in
commit b3a81b6c4fc6 ("HID: i2c-hid: check if device is there before
really probing"), in order to cover devices
based on STM microcontrollers. For touchpads based on STM uC,
the probe sequence needs to take into account the increased response time
for i2c transaction if the device already entered a deep power state.
STM specify the wakeup time as 400us between positive strobe of
the clock line. Deep sleep is controlled by Touchpad FW,
though some devices enter it pretty early to conserve power
in case of lack of activity on the i2c bus.
Failing to follow this requirement will result in touchpad device not being
detected due initial transaction being dropped by STM i2c slave controller.
By adding additional try, first transaction will wake up the touchpad
STM controller, and the second will produce proper detection response.

v1->v2:
* Updated commit message with short sha of a base commit and proper tags
* Rearranged while loop to perform check only once
* Loosened sleeping range

Co-developed-by: Radoslaw Biernacki <rad@xxxxxxxxxxxx>
Signed-off-by: Radoslaw Biernacki <rad@xxxxxxxxxxxx>
Signed-off-by: Lukasz Majczak <lma@xxxxxxxxxxxx>
---
 drivers/hid/i2c-hid/i2c-hid-core.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/hid/i2c-hid/i2c-hid-core.c b/drivers/hid/i2c-hid/i2c-hid-core.c
index 2df1ab3c31cc..ece1a5815e0b 100644
--- a/drivers/hid/i2c-hid/i2c-hid-core.c
+++ b/drivers/hid/i2c-hid/i2c-hid-core.c
@@ -1013,9 +1013,17 @@ static int __i2c_hid_core_probe(struct i2c_hid *ihid)
 	struct i2c_client *client = ihid->client;
 	struct hid_device *hid = ihid->hid;
 	int ret;
+	int tries = 2;
+
+	while (true) {
+		/* Make sure there is something at this address */
+		ret = i2c_smbus_read_byte(client);
+		tries--;
+		if (tries == 0 || ret >= 0)
+			break;
+		usleep_range(400, 500);
+	}
 
-	/* Make sure there is something at this address */
-	ret = i2c_smbus_read_byte(client);
 	if (ret < 0) {
 		i2c_hid_dbg(ihid, "nothing at this address: %d\n", ret);
 		return -ENXIO;
-- 
2.44.0.478.gd926399ef9-goog