linux-kernel - Re: [PATCH v7 2/3] iio: (bma400) add driver for the BMA400

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Date:   Fri, 20 Dec 2019 04:32:20 +0000
From:   Dan Robertson <dan@...obertson.com>
To:     Andy Shevchenko <andy.shevchenko@...il.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>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH v7 2/3] iio: (bma400) add driver for the BMA400

On Thu, Dec 19, 2019 at 01:02:28PM +0200, Andy Shevchenko wrote:
> On Thu, Dec 19, 2019 at 6:27 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.
> 
> ...
> 
> > +static int bma400_set_accel_output_data_rate(struct bma400_data *data,
> > +                                            int hz, int uhz)
> > +{
> > +       unsigned int idx;
> > +       unsigned int odr;
> > +       unsigned int val;
> > +       int ret;
> > +
> > +       if (hz >= BMA400_ACC_ODR_MIN_WHOLE_HZ) {
> > +               if (uhz || hz % BMA400_ACC_ODR_MIN_WHOLE_HZ)
> > +                       return -EINVAL;
> > +
> > +               val = hz / BMA400_ACC_ODR_MIN_WHOLE_HZ;
> 
> Again, AFAICS division may be avoided in both cases (% and / above)
> because of is_power_of_2() check below.
> Can you revisit this?

Yeah I can update this in the next patchset, but I don't know if it is much more
readable this way.

> > +               if (!is_power_of_2(val))
> > +                       return -EINVAL;
> > +
> > +               idx = __ffs(val) + BMA400_ACC_ODR_MIN_RAW + 1;
> > +       } else if (hz == BMA400_ACC_ODR_MIN_HZ && uhz == 500000) {
> > +               idx = BMA400_ACC_ODR_MIN_RAW;
> > +       } else {
> > +               return -EINVAL;
> > +       }
> > +
> > +       ret = regmap_read(data->regmap, BMA400_ACC_CONFIG1_REG, &val);
> > +       if (ret)
> > +               return ret;
> > +
> > +       /* preserve the range and normal mode osr */
> 
> > +       odr = idx | (~BMA400_ACC_ODR_MASK & val);
> 
> Yoda style?

Fixed in v8.

> > +
> > +       ret = regmap_write(data->regmap, BMA400_ACC_CONFIG1_REG, odr);
> > +       if (ret)
> > +               return ret;
> > +
> > +       bma400_output_data_rate_from_raw(idx, &data->sample_freq.hz,
> > +                                        &data->sample_freq.uhz);
> > +       return 0;
> > +}
> ...
> 
> > +int bma400_accel_scale_to_raw(struct bma400_data *data, unsigned int val)
> > +{
> > +       int scale = val / BMA400_SCALE_MIN;
> > +       int raw;
> > +
> > +       if (scale == 0)
> > +               return -EINVAL;
> > +
> > +       raw = __ffs(scale);
> > +
> > +       if (val % BMA400_SCALE_MIN || !is_power_of_2(scale))
> > +               return -EINVAL;
> 
> Ditto.
> 
> > +
> > +       return raw;
> > +}
> 
> ...
> 
> > +out:
> 
> Make a little sense. Why not return directly?

Mostly setup for the next patch in this patchset.

> > +       return ret;
> 
> ...
> 
> > +       ret = bma400_init(data);
> > +       if (ret < 0)
> 
> May it be positive value returned?

Fixed in v8.

Cheers,

 - Dan