Several core ACPI device drivers set acpi_device_class() for the given
struct acpi_device to whatever they like, but that value is never used
unless the driver itself uses it and, sadly, they neglect to clear it on
remove.  Since the only one of them still using acpi_device_class()
after previous changes is the button driver, update the others to stop
setting it in vain.  Also drop the related device class sybmols that
become redundant.

Since the ACPI button driver continues to use acpi_device_class(), make
it clear the struct field represented by acpi_device_class() in its
remove callback.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://patch.msgid.link/3706295.iIbC2pHGDl@rafael.j.wysocki

ACPI drivers usually set acpi_device_name() for the given struct
acpi_device to whatever they like, but that value is never used unless
the driver itself uses it and, quite unfortunately, drivers neglect to
clear it on remove.  Some drivers use it for printing messages or
initializing the names of subordinate devices, but it is better to use
string literals for that, especially if the given one is used just once.

To eliminate unnecessary overhead related to acpi_device_name()
handling, rework multiple core ACPI device drivers to stop setting
acpi_device_name() for struct acpi_device objects manipulated
by them and use a string literal instead of it where applicable.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://patch.msgid.link/10840483.nUPlyArG6x@rafael.j.wysocki

Move the cpuidle driver check from __acpi_processor_start() to
acpi_processor_power_init() which allows variable acpi_idle_driver to
become static.

No intentional functional impact.

Signed-off-by: Huisong Li <lihuisong@huawei.com>
Tested-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://patch.msgid.link/20251223100914.2407069-7-lihuisong@huawei.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Group all of the declarations of functions that belong to the ACPI
processor idle driver together in one place in processor.h.

While at it, drop the unnecessary extern modifier from the declaraions
of two functions.

Signed-off-by: Huisong Li <lihuisong@huawei.com>
Tested-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://patch.msgid.link/20251223100914.2407069-6-lihuisong@huawei.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Notice that acpi_processor_power_init() and acpi_processor_power_exit()
don't need to return any values because their callers don't check them
anyway, so redefine those functions as void.

While at it, rearrange the code in acpi_processor_power_init() to
reduce the indentation level, get rid of a redundant local variable
in that function, and rephrase a code comment in it.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Tested-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://patch.msgid.link/20251223100914.2407069-5-lihuisong@huawei.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Empty stubs are defined in processor.h for some functions provided by
the ACPI processor idle driver, but those functions are only used in
the main ACPI processor driver which requires the ACPI processor idle
driver to be present (selecting CONFIG_ACPI_PROCESSOR causes
CONFIG_ACPI_PROCESSOR_IDLE to be selected too automatically).

This means that the empty stubs in question are not really necessary and
if both CONFIG_ACPI_PROCESSOR and CONFIG_ACPI_PROCESSOR_IDLE are unset,
the compiler complains that they are defined, but not used.  Drop them
to get rid of the compiler warning.

Signed-off-by: Huisong Li <lihuisong@huawei.com>
Tested-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://patch.msgid.link/20251223100914.2407069-3-lihuisong@huawei.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Currently, the ACPI idle driver is registered from within a CPU
hotplug callback. Although this didn't cause any functional issues,
this is questionable and confusing. And it is better to register
the cpuidle driver when all of the CPUs have been brought up.

So add a new function to initialize acpi_idle_driver based on the
power management information of an available CPU and register cpuidle
driver in acpi_processor_driver_init().

This commit has four changes under the commit 7a8c994cbb2d (ACPI:
processor: idle: Optimize ACPI idle driver registration):

 1) move acpi_processor_register_idle_driver() ahead of the
    driver_register().
 2) add acpi_processor_cstate_first_run_checks() before calling
    acpi_processor_get_power_info().
 3) squash the commit 9d68320b2bca (ACPI: processor: idle: Fix
    function defined but not used warning) into this change.
 4) use for_each_possible_cpu(cpu) to scan all possible cpus.

Signed-off-by: Huisong Li <lihuisong@huawei.com>
Tested-by: Borislav Petkov (AMD) <bp@alien8.de>
[ rjw: New comment edits, changelog tweak ]
Link: https://patch.msgid.link/20251223100914.2407069-2-lihuisong@huawei.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Revert commit 7a8c994cbb2d ("ACPI: processor: idle: Optimize ACPI idle
driver registration") because it is reported to introduce a cpuidle
regression leading to a kernel crash on a platform using the ACPI idle
driver.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reported-by: Borislav Petkov <bp@alien8.de>
Tested-by: Borislav Petkov (AMD) <bp@alien8.de>
Closes: https://lore.kernel.org/lkml/20251124200019.GIaSS5U9HhsWBotrQZ@fat_crate.local/

Revert commit 5020d05b3476 ("ACPI: processor: Remove unused empty stubs
of some functions") because it depends on a problematic one.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Revert commit bdf780fbcef5 ("ACPI: processor: idle: Rearrange declarations
in header file") because it depends on a problematic one.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>