linux-kernel - Re: [PATCH V3 3/5] iio: accel: sca3300: modified to support multi chips

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Date:   Thu, 5 May 2022 20:01:22 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     LI Qingwu <qing-wu.li@...ca-geosystems.com.cn>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Rob Herring <robh+dt@...nel.org>,
        Tomas Melin <tomas.melin@...sala.com>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-iio <linux-iio@...r.kernel.org>,
        Rob Herring <robh@...nel.org>
Subject: Re: [PATCH V3 3/5] iio: accel: sca3300: modified to support multi chips

On Thu, May 5, 2022 at 4:12 PM LI Qingwu
<qing-wu.li@...ca-geosystems.com.cn> wrote:
> > -----Original Message-----
> > From: Andy Shevchenko <andy.shevchenko@...il.com>
> > Sent: Wednesday, May 4, 2022 10:39 PM
> > On Wed, May 4, 2022 at 4:35 PM LI Qingwu
> > <qing-wu.li@...ca-geosystems.com.cn> wrote:
> > > > From: Andy Shevchenko <andy.shevchenko@...il.com>
> > > > Sent: Wednesday, May 4, 2022 10:20 PM On Wed, May 4, 2022 at 3:36 PM
> > > > LI Qingwu <Qing-wu.Li@...ca-geosystems.com.cn> wrote:

...

> > > > > +struct sca3300_chip_info {
> > > > > +       const struct iio_chan_spec *channels;
> > > > > +       const int (*accel_scale_table)[2];
> > > > > +       const int *accel_scale_modes_map;
> > > > > +       const unsigned long *scan_masks;
> > > > > +       const int *avail_modes_table;
> > > > > +       const int *freq_modes_map;
> > > > > +       const int *freq_table;
> > > > > +       const u8 num_accel_scales;
> > > > > +       const u8 num_avail_modes;
> > > > > +       const u8 num_channels;
> > > > > +       const u8 num_freqs;
> > > > > +       const u8 chip_id;
> > > >
> > > > Why do you have const qualifier on all members?  The last one is
> > > > understandable, but the rest, esp. pointers should be justified.
> > > Because I thought it was static and has fix value for each chip, unacceptable
> > for you?
> >
> > But why const qualifier? What is the point of it for example for u8 members if
> > the entire object is qualified as const below in the same patch?
> >
> > On top of that, please explain what in your opinion the "const ...
> > *foo" gives us, and what we will lose if we remove the "const" part out of them.
>
> Ah, you are right, those const are unnecessary for nonpointer members.
> for the pointers, the contexts that the pointer points to are still writable.
> what about if I remove all the const from nonpointer and keep it for the pointers?
> Like：
> const struct iio_chan_spec *channels;
> const int (*accel_scale_table)[2];
> const int (*incli_scale_table)[2];
> const int *accel_scale_modes_map;
> const int *incli_scale_modes_map;
> const unsigned long *scan_masks;
> const int *avail_modes_table;
> const int *freq_modes_map;
> const int *freq_table;
> const char *name;
> u8 num_accel_scales;
> u8 num_incli_scales;
> u8 num_avail_modes;
> u8 num_channels;
> u8 num_freqs;
> u8 chip_id;
> bool angle;

It's better, but you still need to justify the rest with explanation
in the commit message.
And I leave this to maintainers to say if the const:s are needed or not.

> > > > > +       const char *name;
> > > > > +};

-- 
With Best Regards,
Andy Shevchenko