[PATCH] HID: i2c-hid: Skip SET_POWER on shutdown for panel followers

[Doug Anderson]

Hi,

On Thu, Sep 3, 2026 at 8:50 PM Justin Yeh <justin.yeh at mediatek.com> wrote:
>
> When an i2c-hid device is a panel follower, drm_atomic_helper_shutdown()
> unprepares the panel before device_shutdown() gets around to the i2c
> client. The panel_unpreparing() callback already calls
> i2c_hid_core_suspend() with force_poweroff set, which sends
> SET_POWER(SLEEP) and then drops the device's regulators.
>
> So by the time i2c_hid_core_shutdown() runs, the controller is unpowered
> and can no longer complete a transfer. On MT8196 the SET_POWER(SLEEP)
> issued there burns the full i2c-mt65xx bus timeout before failing,
> adding two seconds to every reboot.

I don't think there is any guarantee here though, is there? In your
case the panel might have been powered off before
i2c_hid_core_shutdown(), but is there something that ensures that? I'm
not aware of it.

Would it be better to follow in the example of i2c_hid_core_remove()
and just remove ourselves as a panel follower? That would
automatically call the power-off functions if needed, right?

-Doug