Date:   Wed, 29 Dec 2021 17:49:30 +0900
From:   William Breathitt Gray <vilhelm.gray@gmail.com>
To:     Jonathan Cameron <jic23@kernel.org>
Cc:     Lars-Peter Clausen <lars@metafoo.de>,
        Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= 
        <u.kleine-koenig@pengutronix.de>, kernel@pengutronix.de,
        Jonathan Cameron <Jonathan.Cameron@huawei.com>,
        linux-iio@vger.kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org,
        Patrick Havelange <patrick.havelange@essensium.com>,
        Kamel Bouhara <kamel.bouhara@bootlin.com>,
        linux-arm-kernel@lists.infradead.org,
        Syed Nayyar Waris <syednwaris@gmail.com>,
        Oleksij Rempel <linux@rempel-privat.de>,
        Jarkko Nikula <jarkko.nikula@linux.intel.com>,
        David Lechner <david@lechnology.com>,
        Fabrice Gasnier <fabrice.gasnier@foss.st.com>,
        Maxime Coquelin <mcoquelin.stm32@gmail.com>,
        Alexandre Torgue <alexandre.torgue@foss.st.com>,
        linux-stm32@st-md-mailman.stormreply.com,
        Jonathan Corbet <corbet@lwn.net>, linux-doc@vger.kernel.org,
        Ahmad Fatoum <a.fatoum@pengutronix.de>,
        "Felipe Balbi (Intel)" <balbi@kernel.org>,
        Raymond Tan <raymond.tan@intel.com>,
        Benjamin Gaignard <benjamin.gaignard@st.com>
Subject: Re: [PATCH v2 00/23] counter: cleanups and device lifetime fixes
Message-ID: <YcwhGmOdP6QPpB3A@shinobu>
References: <20211227094526.698714-1-u.kleine-koenig@pengutronix.de>
 <c8f6446e-748b-5845-ae60-5d6b8f3e8d39@metafoo.de>
 <20211228173558.3702faa2@jic23-huawei>
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On Tue, Dec 28, 2021 at 05:35:58PM +0000, Jonathan Cameron wrote:
> On Mon, 27 Dec 2021 13:25:25 +0100
> Lars-Peter Clausen <lars@metafoo.de> wrote:
>=20
> > On 12/27/21 10:45 AM, Uwe Kleine-K=C3=B6nig wrote:
> > > [...]
> > >
> > >   - I wonder why counter is a bus and not a class device type. There =
is
> > >     no driver that would ever bind a counter device, is there? So
> > >     /sys/bus/counter/driver is always empty.
> > > =20
> > There used to be a time when GKH said that we do not want new driver=20
> > classes. And all new subsystems should use bus since bus is a superset=
=20
> > of class. This restriction has been eased since then.
> >=20
> > But it was around when the IIO subsystem was merged and since the=20
> > counter subsystem originated from the IIO subsystem I assume it just=20
> > copied this.
> >=20
>=20
> Yup. Discussion about this back then with one view being there
> should never have been class in the first place.
>=20
> https://lore.kernel.org/lkml/4B571DA4.6070603@cam.ac.uk/
>=20
> For anyone who loves the history of these things...
>=20
> FWIW I think Greg suggested IIO should be a bus because we were hanging
> a bunch of different types of device off a class and it was getting messy.
> Kay then gave some history on class vs bus and suggested no new
> subsystem should use class.
>=20
> Ah well, opinions change over time!
>=20
> Also interesting to see we were discussing a bridge to input all that
> time ago and it's still not gone beyond various prototypes (with
> exception of touch screens).
>=20
> Jonathan

Yes this is the reason: Counter subsystem just followed the structure of
the IIO subsystem originally which is how it ended up as a bus; changing
it to a class now would break userspace expectations so that is why it
remains a bus still.

William Breathitt Gray

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