linux-kernel - Re: [PATCH v6 2/2] iio: (bma400) add driver for the BMA400

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Date:   Wed, 11 Dec 2019 15:21:56 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Dan Robertson <dan@...obertson.com>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        linux-iio <linux-iio@...r.kernel.org>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        devicetree <devicetree@...r.kernel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Joe Perches <joe@...ches.com>
Subject: Re: [PATCH v6 2/2] iio: (bma400) add driver for the BMA400

On Wed, Dec 11, 2019 at 3:20 AM Dan Robertson <dan@...obertson.com> wrote:
>
> Add a IIO driver for the Bosch BMA400 3-axes ultra-low power accelerometer.
> The driver supports reading from the acceleration and temperature
> registers. The driver also supports reading and configuring the output data
> rate, oversampling ratio, and scale.

> +#define BMA400_LP_OSR_SHIFT         0x05
> +#define BMA400_NP_OSR_SHIFT         0x04
> +#define BMA400_SCALE_SHIFT          0x06

I'm not sure why this is being defined as hex number instead of plain decimal...

> +#define BMA400_TWO_BITS_MASK        GENMASK(1, 0)
> +#define BMA400_LP_OSR_MASK          GENMASK(6, BMA400_LP_OSR_SHIFT)
> +#define BMA400_NP_OSR_MASK          GENMASK(5, BMA400_NP_OSR_SHIFT)
> +#define BMA400_ACC_ODR_MASK         GENMASK(3, 0)
> +#define BMA400_ACC_SCALE_MASK       GENMASK(7, BMA400_SCALE_SHIFT)

And here simple better to put same numbers. It will help to read.

...

> +extern const struct regmap_config bma400_regmap_config;

> +const struct regmap_config bma400_regmap_config = {
> +       .reg_bits = 8,
> +       .val_bits = 8,
> +       .max_register = BMA400_CMD_REG,
> +       .cache_type = REGCACHE_RBTREE,
> +       .writeable_reg = bma400_is_writable_reg,
> +       .volatile_reg = bma400_is_volatile_reg,
> +};
> +EXPORT_SYMBOL(bma400_regmap_config);

I'm not sure I got the idea why this one is being exported.

...

> +               if (odr < BMA400_ACC_ODR_MIN_RAW ||
> +                   odr > BMA400_ACC_ODR_MAX_RAW) {

One line?

> +                       ret = -EINVAL;
> +                       goto error;
> +               }

...

> +               if (uhz || hz % BMA400_ACC_ODR_MIN_WHOLE_HZ)
> +                       return -EINVAL;
> +
> +               val = hz / BMA400_ACC_ODR_MIN_WHOLE_HZ;
> +               idx = __ffs(val);
> +

> +               if (val ^ BIT(idx))

Seems like funny way of checking is_power_of_2(). But it's up to maintainers.
And your variant may even be better here (in code generation perspective)...

However, the whole idea here is, IIUC, to have something like

  hz = 2^idx * BMA400_ACC_ODR_MIN_WHOLE_HZ

I think you may do it without divisions, i.e. call __ffs() first and then do
   idx = __ffs(...);
   val = hz >> idx;
   if (val != BMA400_ACC_ODR_MIN_WHOLE_HZ)
    return -EINVAL;

or something like above.

> +                       return -EINVAL;

...

> +       odr = (~BMA400_ACC_ODR_MASK & val) | idx;

I'm wondering why Yoda style is being used here.

...

> +static void bma400_accel_scale_from_raw(int raw, unsigned int *val)
> +{
> +       *val = BMA400_SCALE_MIN * (1 << raw);

Isn't it the same as
    *val = BMA400_SCALE_MIN << raw;
?

> +}

...

> +       if (val % BMA400_SCALE_MIN || scale ^ BIT(raw))

Similar comment as above about divisions, is_power_of_2(), etc.

> +               return -EINVAL;

...

> +       ret = regmap_read(data->regmap, BMA400_ACC_CONFIG0_REG, &val);
> +       if (ret < 0)

I'm wondering if in all of these regmap_read()...

> +               return ret;

> +       ret = regmap_write(data->regmap, BMA400_ACC_CONFIG0_REG,
> +                          mode | (val & ~BMA400_TWO_BITS_MASK));
> +       if (ret < 0) {

...and regmap_write() calls you ever can get a positive returned code.

> +               dev_err(data->dev, "Failed to write to power-mode\n");
> +               return ret;
> +       }

...

> +       regmap = devm_regmap_init_i2c(client, &bma400_regmap_config);

> +

Redundant blank line.

> +       if (IS_ERR(regmap)) {
> +               dev_err(&client->dev, "failed to create regmap\n");
> +               return PTR_ERR(regmap);
> +       }

-- 
With Best Regards,
Andy Shevchenko