RE: [PATCH RESEND 0/2] Solve data access delay of ST sensors

[TOSCANELLI Massimo]

Hello Linus and Jonathan

> -----Original Message-----
> From: Linus Walleij <linus.walleij@xxxxxxxxxx>
> Sent: 11 February 2022 02:12
> To: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> Cc: TOSCANELLI Massimo <massimo.toscanelli@xxxxxxxxxxxxxxxxxxxx>;
> linux-kernel@xxxxxxxxxxxxxxx; jic23@xxxxxxxxxx; lars@xxxxxxxxxx;
> caihuoqing@xxxxxxxxx; aardelean@xxxxxxxxxxx;
> andy.shevchenko@xxxxxxxxx; hdegoede@xxxxxxxxxx; LI Qingwu <qing-
> wu.li@xxxxxxxxxxxxxxxxxxxxxxx>; stephan@xxxxxxxxxxx; linux-
> iio@xxxxxxxxxxxxxxx; GEO-CHHER-bsp-development <bsp-
> development.geo@xxxxxxxxxxxxxxxxxxxx>
> 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@xxxxxxxxxx> wrote:
> > On Mon,  7 Feb 2022 09:04:41 +0000
> > Massimo Toscanelli <massimo.toscanelli@xxxxxxxxxxxxxxxxxxxx> 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.
> 
Thanks a lot for your suggestions, I decided to go for the second solution proposed by Jonathan.
Using the buffered interface should be enough, you can discard the patches.

Massimo