linux-kernel - Re: [PATCH v4 2/2] iio: light: as73211: New driver

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Message-ID: <CAHp75VdSNXWCVVgX+8BCC5iWjO14KMUCNrYvZyFfez-fFerQsA@mail.gmail.com>
Date:   Fri, 31 Jul 2020 18:41:47 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Christian Eggers <ceggers@...i.de>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        linux-iio <linux-iio@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 2/2] iio: light: as73211: New driver

On Fri, Jul 31, 2020 at 1:52 PM Christian Eggers <ceggers@...i.de> wrote:

> > W=1 (not V=1) runs kernel doc validation script.
> without V=1, I get nothing. Neither excess nor missing members
> are reported on my system.

It's strange.

...

> > Perhaps add a definition above and comment here?
> >
> > #define AS73211_BASE_FREQ_1024KHZ   1024000
> added similar define in v5. The array looks like the following now
>
> static const int as73211_samp_freq_avail[] = {

>         AS73211_SAMPLE_FREQ_BASE,

' * 1'

>         AS73211_SAMPLE_FREQ_BASE * 2,
>         AS73211_SAMPLE_FREQ_BASE * 4,
>         AS73211_SAMPLE_FREQ_BASE * 8
> };

...

> > > +/* integration time in units of 1024 clock cycles */
> >
> > Unify this with below one. Or the other way around, i.o.w. join one of
> > them into the other.
> >
> > > +static unsigned int as73211_integration_time_1024cyc(struct as73211_data
> > > *data) +{
> > > +       /* integration time in CREG1 is in powers of 2 (x 1024 cycles) */
> > > +       return BIT(FIELD_GET(AS73211_CREG1_TIME_MASK, data->creg1));
> > > +}
> I'm not sure, whether this is possible. as73211_integration_time_1024cyc()
> returns the current setting from hardware. as73211_integration_time_us()
> calculates the resulting time. But as73211_integration_time_us() is also
> called in as73211_integration_time_calc_avail() inside the loop.

What I meant is solely comments to be joined, not the code.

...

> > > +       unsigned int time_us = as73211_integration_time_us(data,
> > > +                                                          as73211_integration_time_1024cyc(data));
> > One line?

> checkpatch complains... ignore?

Hmm... is it over 100? Or you are using some old tools to work with
the kernel...

...

> > > +               /* gain can be calculated from CREG1 as 2^(13 -
> > > CREG1_GAIN) */ +               reg_bits = 13 - ilog2(val);
> >
> > 13 is the second time in the code. Deserves a descriptive definition.

> I'm unsure how to solve this. Possible values for gain:
>
> CREG1[7:4]  | gain
> -----------------------------
> 0           | 2048x
> 1           | 1024x
> 2           |  512x
> ...         |  ...
> 13          |    1x
>
> #define AS73211_CREG1_GAIN_1_NON_SHIFTED 13  // this define is CREG1 related, but not shifted to the right position
>
> static unsigned int as73211_gain(struct as73211_data *data)
> {
>         /* gain can be calculated from CREG1 as 2^(13 - CREG1_GAIN) */
>         return BIT(AS73211_CREG1_GAIN_1_NON_SHIFTED - FIELD_GET(AS73211_CREG1_GAIN_MASK, data->creg1));
> }

This way (w/o _NON_SHIFTED suffix) if both 13:s in the code are of the
same meaning.

...

> > > +       indio_dev->dev.parent = dev;
> >
> > Doesn't IIO core do this for you?
> devm_iio_device_alloc() doesn't pass 'dev' to iio_device_alloc().
> I already looked around, but I didn't find. And after debugging
> v5.4, devm_iio_device_alloc() definitely doesn't do it.

Why are you talking about v5.4? We are in v5.8 cycle contributing to v5.9.

Recently IIO gained some features among which I think the one that
assigns parent devices.

-- 
With Best Regards,
Andy Shevchenko