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

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Message-ID: <20210124132344.7181bd06@archlinux>
Date:   Sun, 24 Jan 2021 13:23:44 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Mike Looijmans <mike.looijmans@...ic.nl>,
        linux-iio <linux-iio@...r.kernel.org>,
        Dan Robertson <dan@...obertson.com>,
        Gaëtan André <rvlander@...tanandre.eu>,
        Jonathan Bakker <xc-racer2@...e.ca>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 2/2] iio: accel: Add support for the Bosch-Sensortec
 BMI088

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

> On Sat, Jan 23, 2021 at 4:35 PM Jonathan Cameron <jic23@...nel.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