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Date: Sun, 28 Apr 2024 14:23:43 +0100
From: Jonathan Cameron <jic23@kernel.org>
To: David Lechner <dlechner@baylibre.com>
Cc: Nuno =?UTF-8?B?U8Oh?= <noname.nuno@gmail.com>, Lars-Peter Clausen
 <lars@metafoo.de>, Michael Hennerich <Michael.Hennerich@analog.com>, Shawn
 Guo <shawnguo@kernel.org>, Sascha Hauer <s.hauer@pengutronix.de>,
 Pengutronix Kernel Team <kernel@pengutronix.de>, Fabio Estevam
 <festevam@gmail.com>, linux-iio@vger.kernel.org,
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 linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 0/3] iio: cleanup masklength usage
Message-ID: <20240428142343.5067c898@jic23-huawei>
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References: <20240425-b4-iio-masklength-cleanup-v1-0-d3d16318274d@baylibre.com>
	<2630ef8c8363b4fa772a2ff2c95cf115ad3c509d.camel@gmail.com>
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On Fri, 26 Apr 2024 10:26:31 -0500
David Lechner <dlechner@baylibre.com> wrote:

> On Fri, Apr 26, 2024 at 2:13=E2=80=AFAM Nuno S=C3=A1 <noname.nuno@gmail.c=
om> wrote:
> >
> > On Thu, 2024-04-25 at 10:03 -0500, David Lechner wrote: =20
> > > While working on other patches I noticed that a few drivers are setti=
ng
> > > the masklength field of struct iio_dev even though it is marked as
> > > [INTERN]. It looks like maybe this was not always the case, but we can
> > > safely clean it up now without breaking anything.
> > >
> > > ---
> > > David Lechner (3):
> > >       iio: adc: ad7266: don't set masklength
> > >       iio: adc: mxs-lradc-adc: don't set masklength
> > >       iio: buffer: initialize masklength accumulator to 0
> > >
> > >  drivers/iio/adc/ad7266.c          | 1 -
> > >  drivers/iio/adc/mxs-lradc-adc.c   | 1 -
> > >  drivers/iio/industrialio-buffer.c | 2 +-
> > >  3 files changed, 1 insertion(+), 3 deletions(-)
> > > ---
> > > base-commit: b80ad8e3cd2712b78b98804d1f59199680d8ed91
> > > change-id: 20240425-b4-iio-masklength-cleanup-86b632b19901
> > > =20
> >
> > Hi David,
> >
> > Nice cleanup. The patches look good to me but there's one thing missing=
 :). As you
> > correctly noted, the field should be internal to the IIO core and drive=
rs should not
> > touch it. Hence, you need to make sure not driver is using it so we can=
 move it into
> > struct iio_dev_opaque [1]. That's the place all the intern fields shoul=
d, eventually,
> > end up.
> >
> > Now, quite some drivers in the trigger handler will read the masklength=
 for looping
> > with for_each_set_bit(). Hence, the straight thing would be an helper t=
o get it.
> > Maybe there's a clever way...
> >
> > I know this is more work than what you had in mind but I think it shoul=
d be fairly
> > simple (hopefully) and since you started it :), maybe we can get the wh=
ole thing done
> > and remove another [INTERN] member from the iio_dev struct.
> >
> > [1]: https://elixir.bootlin.com/linux/latest/source/include/linux/iio/i=
io-opaque.h#L42
> >
> > - Nuno S=C3=A1 =20
>=20
> Sounds like fun. :-p
>=20
> I will look into it.

I think this one might be miss marked as [INTERN]. It should be constant fr=
om the driver
point of view, but given active_scan_masks is meant to be visible to the dr=
iver,
it's length should probably be as well.

Sure every driver should be able to trivially work this out for themselves,=
 but
do we care about stopping them using this?

It might be worth some nice iterator wrappers with names like
iio_for_each_active_channel() though I'd expect those to still be accessing=
 these
fields directly as this is a high performance path so we don't want to to b=
ounce
though a core function to get them.

Jonathan