On Sun, Oct 29, 2017 at 8:48 AM, Viresh Kumar [off-list ref] wrote:

It is possible that some of the resources aren't available at the time
constraints are getting set and the boot constraints core will return
-EPROBE_DEFER for them. In order to retry adding the constraints at a
later point of time (after the resource is added and before any of its
users come up), this patch proposes two things:

- Each constraint is represented by a virtual platform device, so that
  it is re-probed again until the time all the dependencies aren't met.
  The platform device is removed along with the constraint, with help of
  the free_resources() callback.

- Enable early defer probing support by calling
  driver_enable_deferred_probe(), so that the core retries probing
  deferred devices every time any device is bound to a driver. This
  makes sure that the constraint is set before any of the users of the
  resources come up.

What is the effect on boot time? It's highly platform dependent, but
the worst case could be pretty bad I think.

I don't see how this handles the case you mentioned where the amba
pclk gets disabled. It only works if the constraint device is added
before any others, but that is done with initcall level games.

Rob