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

[Chen-Yu Tsai]

On Sun, Jul 5, 2026 at 7:44 AM Dmitry Torokhov
<dmitry.torokhov at gmail.com> wrote:
>
> 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.

I'm a bit confused since you raised the issue for ACPI platforms that don't
go through the regulator API. Now you're saying it's not a big issue?

Either way I will add some new regulator consumer APIs to handle this.
This needs to be in the regulator core to prevent race conditions, such
as when one thread deems the delay is enough just when another disables
the regulator.


ChenYu