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Date:   Sat, 14 May 2022 16:14:56 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Alexandru Ardelean <ardeleanalex@...il.com>
Cc:     LI Qingwu <Qing-wu.Li@...ca-geosystems.com.cn>,
        Lars-Peter Clausen <lars@...afoo.de>,
        mchehab+huawei@...nel.org, linux-iio <linux-iio@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V1 1/5] iio: accel: bmi088: Modified the scale calculate

On Tue, 10 May 2022 09:01:20 +0300
Alexandru Ardelean <ardeleanalex@...il.com> wrote:

> On Mon, May 9, 2022 at 4:46 PM LI Qingwu
> <Qing-wu.Li@...ca-geosystems.com.cn> wrote:
> >
> > The units after application of scale are 100*m/s^2,
> > The scale calculation is only for the device
> > with the range of 3, 6, 12, and 24g,
> > but some other chips have a range of 2, 4, 6, and 8g.
> >
> > Modified the formula to a scale list.
> > The scales in the list are calculated by 1/sensitivity*9.8.
> > The new units after the application of scale are m/s^2.
> >
> > Signed-off-by: LI Qingwu <Qing-wu.Li@...ca-geosystems.com.cn>
> > ---
> >  drivers/iio/accel/bmi088-accel-core.c | 12 +++++++-----
> >  1 file changed, 7 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/iio/accel/bmi088-accel-core.c b/drivers/iio/accel/bmi088-accel-core.c
> > index a06dae5c971d..0c58ffdd00e3 100644
> > --- a/drivers/iio/accel/bmi088-accel-core.c
> > +++ b/drivers/iio/accel/bmi088-accel-core.c
> > @@ -119,6 +119,7 @@ struct bmi088_accel_chip_info {
> >         u8 chip_id;
> >         const struct iio_chan_spec *channels;
> >         int num_channels;
> > +       const int scale_table[4][2];
> >  };
> >
> >  struct bmi088_accel_data {
> > @@ -280,6 +281,7 @@ static int bmi088_accel_read_raw(struct iio_dev *indio_dev,
> >         struct bmi088_accel_data *data = iio_priv(indio_dev);
> >         struct device *dev = regmap_get_device(data->regmap);
> >         int ret;
> > +       int reg;
> >
> >         switch (mask) {
> >         case IIO_CHAN_INFO_RAW:
> > @@ -330,13 +332,12 @@ static int bmi088_accel_read_raw(struct iio_dev *indio_dev,
> >                                 return ret;
> >
> >                         ret = regmap_read(data->regmap,
> > -                                         BMI088_ACCEL_REG_ACC_RANGE, val);
> > +                                         BMI088_ACCEL_REG_ACC_RANGE, &reg);  
> 
> Curios: do we need to validate the value of `reg` here?
> If it goes outside of the 0...3 range, I can see a bit of access
> violation (kernel panic) happening.
> 
> >                         if (ret)
> >                                 goto out_read_raw_pm_put;
> > -
> > -                       *val2 = 15 - (*val & 0x3);
> > -                       *val = 3 * 980;
> > -                       ret = IIO_VAL_FRACTIONAL_LOG2;  
> 
> Not sure what the policy is about changing this now.
> I'll leave this to Jonathan.

It shouldn't be a problem as userspace ABI is a decimal string either way.
Only impact might be on precision and those tend to be minor.

> 
> > +                       *val = data->chip_info->scale_table[reg][0];
> > +                       *val2 = data->chip_info->scale_table[reg][1];
> > +                       ret = IIO_VAL_INT_PLUS_MICRO;
> >
> >                         goto out_read_raw_pm_put;
> >                 default:
> > @@ -432,6 +433,7 @@ static const struct bmi088_accel_chip_info bmi088_accel_chip_info_tbl[] = {
> >                 .chip_id = 0x1E,
> >                 .channels = bmi088_accel_channels,
> >                 .num_channels = ARRAY_SIZE(bmi088_accel_channels),
> > +               .scale_table = {{0, 897}, {0, 1795}, {0, 3590}, {0, 7179}},  
> 
> I like the idea of this scale_table.
> It makes things easier to see (what's happening) without looking into
> the datasheet much.
> 
> >         },
> >  };
> >
> > --
> > 2.25.1
> >  

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