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

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Message-ID: <YcwhGmOdP6QPpB3A@shinobu>
Date:   Wed, 29 Dec 2021 17:49:30 +0900
From:   William Breathitt Gray <vilhelm.gray@...il.com>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     Lars-Peter Clausen <lars@...afoo.de>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, kernel@...gutronix.de,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        linux-iio@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        Patrick Havelange <patrick.havelange@...ensium.com>,
        Kamel Bouhara <kamel.bouhara@...tlin.com>,
        linux-arm-kernel@...ts.infradead.org,
        Syed Nayyar Waris <syednwaris@...il.com>,
        Oleksij Rempel <linux@...pel-privat.de>,
        Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        David Lechner <david@...hnology.com>,
        Fabrice Gasnier <fabrice.gasnier@...s.st.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        linux-stm32@...md-mailman.stormreply.com,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        Ahmad Fatoum <a.fatoum@...gutronix.de>,
        "Felipe Balbi (Intel)" <balbi@...nel.org>,
        Raymond Tan <raymond.tan@...el.com>,
        Benjamin Gaignard <benjamin.gaignard@...com>
Subject: Re: [PATCH v2 00/23] counter: cleanups and device lifetime fixes

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@...afoo.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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