The CXL "root" device, ACPI0017, is an attach point for coordinating
platform level CXL resources and is the parent device for a CXL port
topology tree. As such it has distinct locking rules relative to other
CXL subsystem objects, but because it is an ACPI device the lock class
is established well before it is given to the cxl_acpi driver.

However, the lockdep API does support changing the lock class "live" for
situations like this. Add a device_lock_set_class() helper that a driver
can use in ->probe() to set a custom lock class, and
device_lock_reset_class() to return to the default "no validate" class
before the custom lock class key goes out of scope after ->remove().

Note the helpers are all macros to support dead code elimination in the
CONFIG_PROVE_LOCKING=n case, however device_set_lock_class() still needs
#ifdef CONFIG_PROVE_LOCKING since lockdep_match_class() explicitly does
not have a helper in the CONFIG_PROVE_LOCKING=n case (see comment in
lockdep.h). The lockdep API needs 2 small tweaks to prevent "unused"
warnings for the @key argument to lock_set_class(), and a new
lock_set_novalidate_class() is added to supplement
lockdep_set_novalidate_class() in the cases where the lock class is
converted while the lock is held.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Alison Schofield <alison.schofield@intel.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Ben Widawsky <ben.widawsky@intel.com>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Link: https://lore.kernel.org/r/165100081305.1528964.11138612430659737238.stgit@dwillia2-desk3.amr.corp.intel.comSigned-off-by: Dan Williams <dan.j.williams@intel.com>