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From:   Dmitry Rokosov <DDRokosov@sberdevices.ru>
To:     Andy Shevchenko <andy.shevchenko@gmail.com>
CC:     "robh+dt@kernel.org" <robh+dt@kernel.org>,
        "stano.jakubek@gmail.com" <stano.jakubek@gmail.com>,
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        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        kernel <kernel@sberdevices.ru>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 2/3] iio: add MEMSensing MSA311 3-axis accelerometer
 driver
Thread-Topic: [PATCH v4 2/3] iio: add MEMSensing MSA311 3-axis accelerometer
 driver
Thread-Index: AQHYpzqIoQnaRj7vNkq2cXUUGjAB/62dQgeAgAAYQICAAYT0AIABTNeA
Date:   Fri, 5 Aug 2022 14:19:21 +0000
Message-ID: <20220805141945.sqbhvojckfbmfh7w@CAB-WSD-L081021.sigma.sbrf.ru>
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On Thu, Aug 04, 2022 at 08:28:28PM +0200, Andy Shevchenko wrote:
> > > > +static const struct {
> > > > +       int val;
> > > > +       int val2;
> > > > +} msa311_fs_table[] =3D {
> > > > +       {0, 9580}, {0, 19160}, {0, 38320}, {0, 76641}
> > > > +};
> > >
> > > Besides that this struct is defined not only once in the file, this i=
s
> > > very well NIH struct s32_fract. Why not use the latter?
>=20
> > Good point, but looks like this struct is not so popular in the other
> > kernel drivers:
>=20
> It's simply new, it is not about popularity. I would put it as it's
> not _yet_ so popular.

Okay, no problem. I've already reworked it to s32_fract locally.

>=20
> ...
>=20
> > grep "s32_fract" -r -l . | wc -l
> > 3
>=20
> Hint: `git grep` much much faster on Git repositories (it goes via
> index and not working copy) and see
> `git grep -lw s32_fract`
>=20

Thank you for the hint. Actually I'm using ripgrep for the kernel
fuzzysearching, it's faster than git grep. Here I gave an example based
on grep command, because it's general shell command for the searching
substrings I suppose.

> ...
>=20
> > > > +       .cache_type =3D REGCACHE_RBTREE,
> > >
> > > Tree hash is good for sparse data, do you really have it sparse (a lo=
t
> > > of  big gaps in between)?
> >
> > I suppose so. MSA311 regmap has ~6 gaps.
>=20
> Yes and how long is each gap in comparison to the overall space?

The longest gap is 0xb bytes.
>=20
> ...
>=20
> > > > +       for (fs =3D 0; fs < ARRAY_SIZE(msa311_fs_table); ++fs)
> > >
> > > fs++ will work as well.
> >
> > I would prefer ++fs if you don't mind :)
>=20
> Why? It's a non-standard pattern, and needs an explanation.
>=20

From statistics point of view, you are right :)

$ rg "for" | rg "\+\+[a-z]" | wc -l
7271
$ rg "for" | rg "[a-z]\+\+" | wc -l
81247

[...]

> > > > +                               dev_err(dev, "cannot update freq (%=
d)\n", err);
> > >
> > > frequency
> >
> > It will be more ugly due 80 symbols restriction.
>=20
> Nope, it will be understandable by the user. You do code for the user
> and then for the developer, right?

Sure, that's good point.

[...]

>=20
> ...
>=20
> > > > +               dev_dbg(dev, "found MSA311 compatible chip[%#x]\n",=
 partid);
> > >
> > > Useless message.
> >
> > Why? It's under dynamic debug, so I will see it if I really want to.
>=20
> So what the point of the _successful_ detection? You already know from
> the code, that partid, you know by other means that probe was
> successful, why this message is needed? Especially for debugging when
> we have initcall_debug option.
>=20

Agreed

[...]

--=20
Thank you,
Dmitry=