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From:   Linus Walleij <linus.walleij@linaro.org>
Date:   Sat, 12 Aug 2023 22:40:19 +0200
Message-ID: <CACRpkdYUnpb4oo+4pBxhQqbnquDP_+w3ecGoFX18TTC9BSZFwg@mail.gmail.com>
Subject: Re: [PATCH 1/2] iio: lsm6dsx: Support temperature channel
To:     Lorenzo Bianconi <lorenzo@kernel.org>
Cc:     Jonathan Cameron <jic23@kernel.org>,
        Lars-Peter Clausen <lars@metafoo.de>,
        Mario Tesi <mario.tesi@st.com>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org
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On Sat, Aug 12, 2023 at 11:17=E2=80=AFAM Lorenzo Bianconi <lorenzo@kernel.o=
rg> wrote:

> > > looking at the ISM330DHCX datasheet, the temperature sensor ODR is ju=
st 52Hz,
> > > while values in 0x0A register are used only for FIFO decimation, they=
 are not
> > > values you can configure the sensor e.g. for read_one_shot().

BTW looked at this and the read_one_shot() call uses
register 0x20/0x21 as appropriate.

> > >
> > > > +                             .odr_avl[0] =3D {  26000, 0x02 },
> > > > +                             .odr_avl[1] =3D {  52000, 0x03 },
> > > > +                             .odr_len =3D 2,
> >
> > I look at page 44, paragraph 9.6 about bits 4-5:
> >
> > ODR_T_BATCH_[1:0]
> > Selects batch data rate (write frequency in FIFO) for temperature data
> > (00: Temperature not batched in FIFO (default);
> > 01: 1.6 Hz;
> > 10: 12.5 Hz;
> > 11: 52 Hz)
>
> AFAIR the batch register is used to sub-sample sensor data before queuein=
g them
> into the FIFO (please check st_lsm6dsx_set_fifo_odr()), but it does not r=
efer
> to the configured sensor ODR.
> Looking at the device application-note [0], the temperature sensor ODR de=
pends
> on the accel/gyro one:
>
> - temperature sensor ODR =3D=3D accel sensor ODR if accel ODR is < 52Hz a=
nd the
>   gyro is in power-down
> - temperature sensor ODR =3D 52Hz if accel ODR > 52Hz or if the gyro is n=
ot in
>   power-down

We handle the TEMP along with the EXT channels in
st_lsm6dsx_set_odr() which actually makes sure to match
the data rate of the accelerometer.

It looks as nobody cared to look into the issue with the
gyroscope though :/ It feels like a whole separate issue,
I expect more channels to be affected by that...

Yours,
Linus Walleij