Re: [PATCH v3 6/9] i2c: of-prober: Defer regulator_disable() on successful probe in simple helper

[Chen-Yu Tsai]

On Tue, Jul 21, 2026 at 6:24 PM Andy Shevchenko
<andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
>
> On Tue, Jul 21, 2026 at 03:52:20PM +0800, Chen-Yu Tsai wrote:
> > When a I2C component is found, it's device node is immediately enabled.
> > This triggers device creation and driver binding. The prober will hold
> > the regulator enable reference across this part. If the driver probes
> > synchronously, then it happens within this window. On the other hand,
> > if the driver probes asynchronously, there is high chance that it
> > happens after the prober's cleanup function was called, in which case
> > the regulator would have been disabled when the driver's probe function
> > is called. This would then require the driver to wait 100 ms for the
> > hardware to reinitialize, even if the probe function was just a split
> > second late and the regulator was disabled a few milliseconds ago.
> >
> > Recently, some of the drivers for the component that are targeted by the
> > I2C OF component prober gained the ability to skip waiting for hardware
> > initialization if the regulator was left enabled. This happens when the
> > PMIC has them on by default, or if the component prober left them on
> > after probing the component.
> >
> > Wait a bit of time before dropping the enable refcount on our end so
> > that the actual driver has the opportunity to catch and increase the
> > refcount on their end. The 100 ms delay was arbitrarily chosen.
>
> ...
>
> > +     /*
> > +      * Wait a bit of time for async drivers to probe and increase the
> > +      * regulator enable count. This allows the drivers to check and
> > +      * skip waiting for re-initialization.
> > +      */
> > +     if (defer_disable) {
> > +             dev_dbg(dev, "Deferring regulator disable\n");
> > +             msleep(100);
>
> How was this value chosen?

I just chose an arbitrary round value.

If both the prober and the driver for the probed device (trackpad in
this example) are builtin, the time between enabling the node and the
driver asynchronously probing is between 5 ms and 30 ms, but could
also see outliers exceeding 100 ms.

If you're worried the value won't suit every user, I could make it a
parameter of the simple helpers? And the user itself could be made to
probe asynchronously to not block the main code path.


ChenYu