Re: [PATCH v2 00/23] counter: cleanups and device lifetime fixes

From: William Breathitt Gray <vilhelm.gray@gmail.com>
To: Jonathan Cameron <jic23@kernel.org>
Cc: "Lars-Peter Clausen" <lars@metafoo.de>,
	"Uwe Kleine-König" <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
Date: Wed, 29 Dec 2021 17:49:30 +0900	[thread overview]
Message-ID: <YcwhGmOdP6QPpB3A@shinobu> (raw)
In-Reply-To: <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:
> 
> > On 12/27/21 10:45 AM, Uwe Kleine-König 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.
> > >  
> > There used to be a time when GKH said that we do not want new driver 
> > classes. And all new subsystems should use bus since bus is a superset 
> > of class. This restriction has been eased since then.
> > 
> > But it was around when the IIO subsystem was merged and since the 
> > counter subsystem originated from the IIO subsystem I assume it just 
> > copied this.
> > 
> 
> Yup. Discussion about this back then with one view being there
> should never have been class in the first place.
> 
> https://lore.kernel.org/lkml/4B571DA4.6070603@cam.ac.uk/
> 
> For anyone who loves the history of these things...
> 
> 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.
> 
> Ah well, opinions change over time!
> 
> 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).
> 
> 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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