Re: [PATCH 2/2] HID: i2c-hid: Add a quirk to keep the power in shutdown

[Jiri Kosina <jikos@kernel.org>]

On Thu, 7 Jan 2021, Hui Wang wrote:

> >> On the latest Thinkpad Yoga laptop, the touchscreen module is wacom
> >> I2C WACF2200 (056a:5276), we found the touchscreen could not work
> >> after rebooting, needs to poweroff the machine then poweron the
> >> machine to let it work.
> >>
> >> It is highly possible that this is a BIOS issue, but the windows
> >> doesn't have this problem with the same BIOS.
> >>
> >> If keeping the power on when calling shutdown, the touchscreen could
> >> work after rebooting. Let us add a quirk for it and apply the quirk
> >> to this machine only.
> > I wonder what do Windows do differently here. Perhaps they never put the
> > i2c device to sleep while in shutdown anyway? Is there any downside to
> > (not) doing the same?
> 
> It is highly possible the Windows doesn't sleep the i2c device in shutdown.
> When calling shutdown, it usually means reboot or poweroff the machine, so the
> sleep is meaningless in this situation. In other situations like users
> manually unload the i2c driver, maybe it will add a bit power consumption
> without sleeping the device.

Agreed, but if windows really don't put the device to sleep before 
shutting down, odds are there will be more devices behaving the same, and 
therefore we'd rather make it the default case instead of growing just 
another quirk list.

> Anyway, I will try to ask for help from vendor, maybe they could provide 
> how Windows do when shutdown.

Thank you,

-- 
Jiri Kosina
SUSE Labs