In commit 18eeef46d3 ("HID: i2c-hid: goodix: Tie the reset line to
true state of the regulator"), we started tying the reset line of
Goodix touchscreens to the regulator.
The primary motivation for that patch was some pre-production hardware
(specifically sc7180-trogdor-homestar) where it was proposed to hook
the touchscreen's main 3.3V power rail to an always-on supply. In such
a case, when we turned "off" the touchscreen in Linux it was bad to
assert the "reset" GPIO because that was causing a power drain. The
patch accomplished that goal and did it in a general sort of way that
didn't require special properties to be added in the device tree for
homestar.
It turns out that the design of using an always-on power rail for the
touchscreen was rejected soon after the patch was written and long
before sc7180-trogdor-homestar went into production. The final design
of homestar actually fully separates the rail for the touchscreen and
the display panel and both can be powered off and on. That means that
the original motivation for the feature is gone.
There are 3 other users of the goodix i2c-hid driver in mainline.
I'll first talk about 2 of the other users in mainline: coachz and
mrbland. On both coachz and mrbland the touchscreen power and panel
power _are_ shared. That means that the patch to tie the reset line to
the true state of the regulator _is_ doing something on those
boards. Specifically, the patch reduced power consumption by tens of
mA in the case where we turned the touchscreen off but left the panel
on. Other than saving a small bit of power, the patch wasn't truly
necessary. That being said, even though a small bit of power was saved
in the state of "panel on + touchscreen off", that's not actually a
state we ever expect to be in, except perhaps for very short periods
of time at boot or during suspend/resume. Thus, the patch is truly not
necessary. It should be further noted that, as documented in the
original patch, the current code still didn't optimize power for every
corner case of the "shared rail" situation.
The last user in mainline was very recently added: evoker. Evoker is
actually the motivation for me removing this bit of code. It turns out
that for evoker we need to manage a second power rail for IO to the
touchscreen. Trying to fit the management of this IO rail into the
regulator notifiers turns out to be extremely hard. To avoid lockdep
splats you shouldn't enable/disable other regulators in regulator
notifiers and trying to find a way around this was going to be fairly
difficult.
Given the lack of any true motivation to tie the reset line to the
regulator, lets go back to the simpler days and remove the code. This
is, effectively, a revert of commit bdbc65eb77 ("HID: i2c-hid:
goodix: Fix a lockdep splat"), commit 25ddd7cfc5 ("HID: i2c-hid:
goodix: Use the devm variant of regulator_register_notifier()"), and
commit 18eeef46d3 ("HID: i2c-hid: goodix: Tie the reset line to true
state of the regulator").
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Link: https://lore.kernel.org/r/20230206184744.4.I085b32b6140c7d1ac4e7e97b712bff9dd5962b62@changeid
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
557e05fa9f