linux-kernel - Re: [PATCH RESEND 0/2] Solve data access delay of ST sensors

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Date:   Fri, 11 Feb 2022 02:12:22 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc:     Massimo Toscanelli <massimo.toscanelli@...ca-geosystems.com>,
        linux-kernel@...r.kernel.org, jic23@...nel.org, lars@...afoo.de,
        caihuoqing@...du.com, aardelean@...iqon.com,
        andy.shevchenko@...il.com, hdegoede@...hat.com,
        Qing-wu.Li@...ca-geosystems.com.cn, stephan@...hold.net,
        linux-iio@...r.kernel.org, bsp-development.geo@...ca-geosystems.com
Subject: Re: [PATCH RESEND 0/2] Solve data access delay of ST sensors

On Mon, Feb 7, 2022 at 2:59 PM Jonathan Cameron
<Jonathan.Cameron@...wei.com> wrote:
> On Mon,  7 Feb 2022 09:04:41 +0000
> Massimo Toscanelli <massimo.toscanelli@...ca-geosystems.com> wrote:

> The standard approach to avoiding rapid power up and power down cycles
> is to use runtime_pm with autosuspend and a period set at a period
> of perhaps 1 second.  Would that work for you?  You'll pay the costs
> of power up only on the first read after a period of not reading.
>
> Exposing the control to userspace for this sort of thing is normally
> a bad idea because userspace generally has no idea if it should use it
> as there is no clean way of telling userspace the costs of not using
> it (as those will be device specific).
>
> If you have a usecase that requires regular reading you should also
> think about whether using the buffered interface is more appropriate.
> IIRC that will keep these devices powered up continuously whilst
> the buffer is enabled and will provide a lower overhead way of
> reading data than sysfs reads.

I see that I have repeted similar comments.

Sorry for the hammering.

I agree with Jonathan's stance here.

Yours,
Linus Walleij