Re: [PATCH v6 2/2] iio: accel: Add support for the Bosch-Sensortec BMI088

Jonathan Cameron
2021-01-24T13:24:52Z

On Sun, 24 Jan 2021 00:21:13 +0100
Linus Walleij <linus.walleij@linaro.org> wrote:

> On Sat, Jan 23, 2021 at 4:35 PM Jonathan Cameron <jic23@kernel.org> wrote:
> > [Me]
> > > Next, I think it is better to let suspend/resume, i.e. system PM
> > > reuse runtime PM since you're implementing that. This is why
> > > we invented PM runtime force resume and force suspend.
> >
> > Here the driver is turning more off for full suspend than in the
> > runtime path. If that results in significant extra delay then
> > it's not appropriate to have that in the runtime suspend path.
>
> I see the point.
>
> The resume path calls bmi088_accel_enable() which incurs
> a 5ms delay.
>
> The runtime resume path incurs a 1 ms delay.
>
> The runtime autosuspend kicks in after 2 ms.
>
> > Maybe the simplification of not doing the deeper power saving
> > mode is worth the extra power cost or extra delay, but
> > I'm not yet convinced.
>
> I would personally set the autosuspend to ~20ms and just use
> one path and take a hit of 5 ms whenever we go down between
> measures if it is a system that is for human interaction, but for
> control systems this more complex set-up may be better for
> response latencies.
>
> The current approach may be better tuned to perfection and
> we are all perfectionists :D
>
> I'm just worrying a little about bugs and maintainability.
Fully understood. Though for things like this I like to leave
it at the discretion of the driver author as fairly safe they
are a user of the device.

May well make sense to go with the longer times as you
suggest though! Over to you Mike :)

Jonathan

>
> Yours,
> Linus Walleij