regulator: Defer init completion for a while after late_initcall

regulator: Defer init completion for a while after late_initcall

The kernel has no way of knowing when we have finished instantiating
drivers, between deferred probe and systems that build key drivers as
modules we might be doing this long after userspace has booted. This has
always been a bit of an issue with regulator_init_complete since it can
power off hardware that's not had it's driver loaded which can result in
user visible effects, the main case is powering off displays. Practically
speaking it's not been an issue in real systems since most systems that
use the regulator API are embedded and build in key drivers anyway but
with Arm laptops coming on the market it's becoming more of an issue so
let's do something about it.

In the absence of any better idea just defer the powering off for 30s
after late_initcall(), this is obviously a hack but it should mask the
issue for now and it's no more arbitrary than late_initcall() itself.
Ideally we'd have some heuristics to detect if we're on an affected
system and tune or skip the delay appropriately, and there may be some
need for a command line option to be added.

Link: https://lore.kernel.org/r/20190904124250.25844-1-broonie@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>
Tested-by: Lee Jones <lee.jones@linaro.org>
Cc: stable@vger.kernel.org