HID: i2c-hid: goodix: Stop tying the reset line to the regulator
In commit 18eeef46 ("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 bdbc65eb77ee ("HID: i2c-hid: goodix: Fix a lockdep splat"), commit 25ddd7cf ("HID: i2c-hid: goodix: Use the devm variant of regulator_register_notifier()"), and commit 18eeef46 ("HID: i2c-hid: goodix: Tie the reset line to true state of the regulator"). Signed-off-by: NDouglas Anderson <dianders@chromium.org> Reviewed-by: NMatthias Kaehlcke <mka@chromium.org> Reviewed-by: NDmitry Torokhov <dmitry.torokhov@gmail.com> Link: https://lore.kernel.org/r/20230206184744.4.I085b32b6140c7d1ac4e7e97b712bff9dd5962b62@changeidSigned-off-by: NBenjamin Tissoires <benjamin.tissoires@redhat.com>
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