linux-kernel - Re: [PATCH] iio: st_sensors: Fix the sleep time for sampling

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Date:   Tue, 27 Nov 2018 15:23:04 +0800
From:   Jian-Hong Pan <jian-hong@...lessm.com>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     Denis Ciocca <denis.ciocca@...com>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        linux-iio@...r.kernel.org,
        Linux Kernel <linux-kernel@...r.kernel.org>, linux@...lessm.com
Subject: Re: [PATCH] iio: st_sensors: Fix the sleep time for sampling

Jonathan Cameron <jic23@...nel.org> 於 2018年11月25日 週日 下午9:23寫道：
>
> On Wed, 21 Nov 2018 13:13:40 +0800
> Jian-Hong Pan <jian-hong@...lessm.com> wrote:
>
> > Denis CIOCCA <denis.ciocca@...com> 於 2018年11月20日 週二 上午3:05寫道：
> > >
> > > Hi Jian,
> > >
> > > Not clear to me why should be + instead of *.
> > >
> > > ODR is expressed in Hz, so (1/Hz) = period in seconds (1 sample sampling time) [s]
> > > 1000 * (1/Hz) = period in milliseconds (1 sample sampling time) [ms]
> > > n * 1000 * (1/Hz) = n times period in milliseconds (n times sample sampling time) [ms]
> > >
> > > In your case you assume bootime is in milliseconds.
> >
> > Yes, I assume that according to the original comment.
> >
> > >Maybe we can change the comment and use 'number of samples ...'.
> >
> > Making the meaning more clear is better.
> >
> > However, does the bootime of the measurement need as the long time to
> > be enabled?
> > If the sampling rate is 1Hz and n is 2, then they will do msleep with
> > 2000 ms for each st_sensors_read_info_raw.
>
> Superficially that seems correct as we need to be sure that a reading
> has occurred.  If you want it to be quicker than the ODR should be set
> faster so that the reading shows up reasonably quickly. At 1Hz and
> you want to drop 2 samples, it will indeed take 2 seconds.

Now, I understand with the description.  Thank you.

Jian-Hong Pan

> > > -----Original Message-----
> > > From: linux-iio-owner@...r.kernel.org <linux-iio-owner@...r.kernel.org> On Behalf Of Jian-Hong Pan
> > > Sent: Sunday, November 18, 2018 10:12 PM
> > > To: Jonathan Cameron <jic23@...nel.org>; Hartmut Knaack <knaack.h@....de>; Lars-Peter Clausen <lars@...afoo.de>; Peter Meerwald-Stadler <pmeerw@...erw.net>; Dominique Martinet <asmadeus@...ewreck.org>
> > > Cc: linux-iio@...r.kernel.org; linux-kernel@...r.kernel.org; linux@...lessm.com; Jian-Hong Pan <jian-hong@...lessm.com>
> > > Subject: [PATCH] iio: st_sensors: Fix the sleep time for sampling
> > >
> > > According to the description of st_sensor_settings and st_sensor_data structures' comments:
> > > - bootime: samples to discard when sensor passing from power-down to power-up.
> > > - odr: Output data rate of the sensor [Hz].
> > >
> > > The sleep time should be
> > > sdata->sensor_settings->bootime + 1000 / sdata->odr ms.
> > >
> > > Signed-off-by: Jian-Hong Pan <jian-hong@...lessm.com>
> > > ---
> > >  drivers/iio/common/st_sensors/st_sensors_core.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/iio/common/st_sensors/st_sensors_core.c b/drivers/iio/common/st_sensors/st_sensors_core.c
> > > index 26fbd1bd9413..6b87ea657a92 100644
> > > --- a/drivers/iio/common/st_sensors/st_sensors_core.c
> > > +++ b/drivers/iio/common/st_sensors/st_sensors_core.c
> > > @@ -594,7 +594,7 @@ int st_sensors_read_info_raw(struct iio_dev *indio_dev,
> > >                 if (err < 0)
> > >                         goto out;
> > >
> > > -               msleep((sdata->sensor_settings->bootime * 1000) / sdata->odr);
> > > +               msleep(sdata->sensor_settings->bootime + 1000 / sdata->odr);
> > >                 err = st_sensors_read_axis_data(indio_dev, ch, val);
> > >                 if (err < 0)
> > >                         goto out;
> > > --
> > > 2.11.0
> > >
>