linux-kernel - Re: [PATCH 1/2] iio: lsm6dsx: Support temperature channel

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Date:   Mon, 28 Aug 2023 17:43:32 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Lorenzo Bianconi <lorenzo@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Mario Tesi <mario.tesi@...com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] iio: lsm6dsx: Support temperature channel

On Sat, 12 Aug 2023 22:40:19 +0200
Linus Walleij <linus.walleij@...aro.org> wrote:

> On Sat, Aug 12, 2023 at 11:17 AM Lorenzo Bianconi <lorenzo@...nel.org> wrote:
> 
> > > > looking at the ISM330DHCX datasheet, the temperature sensor ODR is just 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] = {  26000, 0x02 },
> > > > > +                             .odr_avl[1] = {  52000, 0x03 },
> > > > > +                             .odr_len = 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 queueing them
> > into the FIFO (please check st_lsm6dsx_set_fifo_odr()), but it does not refer
> > to the configured sensor ODR.
> > Looking at the device application-note [0], the temperature sensor ODR depends
> > on the accel/gyro one:
> >
> > - temperature sensor ODR == accel sensor ODR if accel ODR is < 52Hz and the
> >   gyro is in power-down
> > - temperature sensor ODR = 52Hz if accel ODR > 52Hz or if the gyro is not 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
FWIW this seems crazy.  Ah well, Lorenzo is the expert on these beasts.

Jonathna