linux-kernel - Re: [PATCH] iio: sx9310: Prefer async probe

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Date:   Tue, 01 Sep 2020 00:03:55 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Doug Anderson <dianders@...omium.org>,
        Jonathan Cameron <jic23@...nel.org>
Cc:     Alexandru Ardelean <alexandru.ardelean@...log.com>,
        Daniel Campello <campello@...omium.org>,
        Enrico Granata <egranata@...omium.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        linux-iio <linux-iio@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dmitry Torokhov <dtor@...omium.org>
Subject: Re: [PATCH] iio: sx9310: Prefer async probe

Quoting Doug Anderson (2020-08-31 11:59:37)
> On Sat, Aug 29, 2020 at 10:18 AM Jonathan Cameron <jic23@...nel.org> wrote:
> > Agreed. However, I'd like a comment next to the place we turn it on
> > saying what delays we are trying to mitigate by enabling it in this
> > driver.
> 
> OK, I used function graph to get a trace.  Some of the time is simply
> i2c transfers, which we do A LOT of during initialization (and i2c
> transfers aren't known for being instant).  However, that's not the
> big problem.  Check out the regmap_read_poll_timeout() in
> sx9310_init_compensation().  20 ms per sleep with a 2 second timeout.
> This seems to eat over around 220 ms of the time on my system.
> 
> So how do you want to do this?  Do you want me to re-post the patch
> and mention the regmap_read_poll_timeout() in the commit message?  Do
> you want to just add that to the commit message yourself?
> 

I think the suggestion is to put a comment next to the
PROBE_PREFER_ASYNCHRONOUS flag indicating that
sx9310_init_compensation() can take a while. Should the compensation be
delayed even further though to some time when userspace opens the device
node?