Re: [PATCH v2 1/7] Input: elan_i2c - Wait for initialization after enabling regulator supply

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

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