From 76a2fd54b32a57c0feae03168252672478904e53 Mon Sep 17 00:00:00 2001 From: Brendan McGrath Date: Sat, 7 Jan 2017 08:01:38 +1100 Subject: [PATCH] HID: i2c-hid: Add sleep between POWER ON and RESET Support for the Asus Touchpad was recently added. It turns out this device can fail initialisation (and become unusable) when the RESET command is sent too soon after the POWER ON command. Unfortunately the i2c-hid specification does not specify the need for a delay between these two commands. But it was discovered the Windows driver has a 1ms delay. As a result, this patch modifies the i2c-hid module to add a sleep inbetween the POWER ON and RESET commands which lasts between 1ms and 5ms. See https://github.com/vlasenko/hid-asus-dkms/issues/24 for further details. Signed-off-by: Brendan McGrath Reviewed-by: Benjamin Tissoires Signed-off-by: Jiri Kosina --- drivers/hid/i2c-hid/i2c-hid.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/drivers/hid/i2c-hid/i2c-hid.c b/drivers/hid/i2c-hid/i2c-hid.c index 78fb32a7b1034..ea3c3546cef7f 100644 --- a/drivers/hid/i2c-hid/i2c-hid.c +++ b/drivers/hid/i2c-hid/i2c-hid.c @@ -426,6 +426,15 @@ static int i2c_hid_hwreset(struct i2c_client *client) if (ret) goto out_unlock; + /* + * The HID over I2C specification states that if a DEVICE needs time + * after the PWR_ON request, it should utilise CLOCK stretching. + * However, it has been observered that the Windows driver provides a + * 1ms sleep between the PWR_ON and RESET requests and that some devices + * rely on this. + */ + usleep_range(1000, 5000); + i2c_hid_dbg(ihid, "resetting...\n"); ret = i2c_hid_command(client, &hid_reset_cmd, NULL, 0); -- 2.39.5