Hi Chen-Yu,

On Fri, Jul 03, 2026 at 07:55:54PM +0800, Chen-Yu Tsai wrote:

Elan trackpad controllers require some delay after enabling power to
the controller for the hardware and firmware to initialize:

  - 2ms for hardware initialization
  - 100ms for firmware initialization

Until then, the hardware will not respond to I2C transfers. This was
observed on the MT8173 Chromebooks after the regulator supply for the
trackpad was changed to "not always on".

Add proper delays after regulator_enable() calls. To avoid impacting
the boot time of existing devices that have the power rails always on,
skip the delay if the regulator supply was already enabled. In this
case the regulator is either always on, was on by default at power up,
or was left on by some other driver, such as the I2C OF component
prober. Either way the controller has had ample time to initialize.

Unfortunately we do not know that [it had ample time]. For this code be
reliable we need to record the time at which given regulator was turned
on and then execute/adjust the delay as needed. Until we have it we need
to assume the regulator was enabled at the time of regulator_enable()
call.

I am not concerned with increased boot time too much given the driver is
set up for asynchronous probing.

Thanks.

-- 
Dmitry