On Jan 07 2017 or thereabouts, Brendan McGrath wrote: > 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 <redmcg@xxxxxxxxxxxxxxxxxxx> > --- > Changes since v2: > - added comments to explain the reason for the sleep > Looks good now, thanks! Reviewed-by: Benjamin Tissoires <benjamin.tissoires@xxxxxxxxxx> Cheers, Benjamin > 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 844662c..d5288f3 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); > -- > 2.7.4 > -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
