linux-kernel - Re: [PATCH V1 1/5] iio: accel: bmi088: Modified the scale calculate

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Message-ID: <CA+U=DspAJMq7hp9RixzZcjW=rR7tEMdrHuyS23cgjmq62vmPeA@mail.gmail.com>
Date:   Tue, 10 May 2022 09:01:20 +0300
From:   Alexandru Ardelean <ardeleanalex@...il.com>
To:     LI Qingwu <Qing-wu.Li@...ca-geosystems.com.cn>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        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 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.

> +                       *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
>