[PATCH v1 10/10] ACPI: Convert button and battery drivers to platform ones

["Rafael J. Wysocki" <rafael@kernel.org>]

Hi All,

While binding drivers directly to struct acpi_device objects allows
basic functionality to be provided, at least in the majority of cases,
there are some problems with it, related to general consistency, sysfs
layout, power management operation ordering, and code cleanliness.

First of all, struct acpi_device objects represent firmware entities
rather than hardware and in many cases they provide auxiliary information
on devices enumerated independently (like PCI devices or CPUs).  It is
therefore generally questionable to assign resources to them or create
class devices and similar under them because they don't provide
functionality associated with those entities by themselves (for example,
they don't generate wakeup or input events).

As a general rule, a struct acpi_device can only be a parent of another
struct acpi_device.  If that's not the case, the location of the child
device in the device hierarchy is at least confusing and it may not be
straightforward to identify the piece of hardware corresponding to that
device.

Using system suspend and resume callbacks directly with struct acpi_device
objects is questionable either because it may cause ordering problems to
happen.  Namely, struct acpi_device objects are registered before any
devices corresponded to by them and they land on the PM list before all
of those devices.  Consequently, the execution ordering of their PM
callbacks may be different from what is generally expected.  Moreover,
dependencies returned by _DEP objects don't generally affect struct
acpi_device objects themselves, only the "physical" device objects
associated with them, which potentially is one more source of inconsistency.

All of the above means that binding drivers to struct acpi_device "devices"
should generally be avoided and so this series converts three generic ACPI
device drivers, the button driver, the tiny power button driver, and the
battery driver, to platform drivers.

Patches [01-03/10] are preliminary for the button driver conversions.  Patch
[01/10] causes platform devices to be registered for "fixed event device"
buttons, patch [02/10] cleans up the "fixed event device" registration code,
and patch [03/10] rearranges the notification handling code in the button
driver to use internal "button" structures for passing data instead of
struct acpi_device objects.

Patches [04-05/10] convert the two button drivers to platform ones and
patches [06-07/10] do some cleanups on top of them.

Patches [08-09/10] are preliminary for the battery driver conversion which
is carried out in patch [10/10].

Thanks!