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 [off-list ref] wrote:

quoted

On 12/27/21 10:45 AM, Uwe Kleine-König wrote:

quoted

[...]

  - 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/ (local)

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