power_supply core has the bad habit of calling our battery callbacks
from within power_supply_register(). Furthermore, if the callbacks
fail with an unhandled error code, it will skip any uevent that it
might currently process.
So if HID-core registers battery devices, an "add" uevent is generated
and the battery callbacks are called. These will gracefully fail due
to timeouts as they might still hold locks on event processing. One
could argue that this should be fixed in power_supply core, but the
least we can do is to signal ENODATA so power_supply core will just
skip the property and continue with the uevent.

This fixes a bug where "add" and "remove" uevents are skipped for
battery devices. upower is unable to track these devices and currently
needs to ignore them.

This patch also overwrites any other error code. I cannot see any reason
why we should forward protocol- or I/O-errors to the power_supply core.
We handle these errors in hid_ll_driver later, anyway, so just skip
them. power_supply core cannot do anything useful with them, anyway,
and we avoid skipping important uevents and confusing user-space.

Thanks a lot to Daniel Nicoletti for pushing and investigating
on this.

Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Anton Vorontsov <cbou@mail.ru>
Cc: David Woodhouse <dwmw2@infradead.org>
Reported-by: NDaniel Nicoletti <dantti12@gmail.com>
Signed-off-by: NDavid Herrmann <dh.herrmann@gmail.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>