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@xxxxxxxxxx> 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@xxxxxxxxx/ > > 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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