ACPI / processor: Avoid reserving IO regions too early

Roland Dreier reports that one of his systems cannot boot because of
the changes made by commit ac212b6980d8 (ACPI / processor: Use common
hotplug infrastructure).

The problematic part of it is the request_region() call in
acpi_processor_get_info() that used to run at module init time before
the above commit and now it runs much earlier.  Unfortunately, the
region(s) reserved by it fall into a range the PCI subsystem attempts
to reserve for AHCI IO BARs.  As a result, the PCI reservation fails
and AHCI doesn't work, while previously the PCI reservation would
be made before acpi_processor_get_info() and it would succeed.

That request_region() call, however, was overlooked by commit
ac212b6980d8, as it is not necessary for the enumeration of the
processors.  It only is needed when the ACPI processor driver
actually attempts to handle them which doesn't happen before
loading the ACPI processor driver module.  Therefore that call
should have been moved from acpi_processor_get_info() into that
module.

Address the problem by moving the request_region() call in question
out of acpi_processor_get_info() and use the observation that the
region reserved by it is only needed if the FADT-based CPU
throttling method is going to be used, which means that it should
be sufficient to invoke it from acpi_processor_get_throttling_fadt().

Fixes: ac212b6980d8 (ACPI / processor: Use common hotplug infrastructure)
Reported-by: Roland Dreier <roland@purestorage.com>
Tested-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/acpi_processor.c

@@ -331,15 +331,6 @@ static int acpi_processor_get_info(struct acpi_device *device)
 		pr->throttling.duty_width = acpi_gbl_FADT.duty_width;
 
 		pr->pblk = object.processor.pblk_address;
-
-		/*
-		 * We don't care about error returns - we just try to mark
-		 * these reserved so that nobody else is confused into thinking
-		 * that this region might be unused..
-		 *
-		 * (In particular, allocating the IO range for Cardbus)
-		 */
-		request_region(pr->throttling.address, 6, "ACPI CPU throttle");
 	}
 
 	/*

drivers/acpi/processor_throttling.c

@@ -676,6 +676,15 @@ static int acpi_processor_get_throttling_fadt(struct acpi_processor *pr)
 	if (!pr->flags.throttling)
 		return -ENODEV;
 
+	/*
+	 * We don't care about error returns - we just try to mark
+	 * these reserved so that nobody else is confused into thinking
+	 * that this region might be unused..
+	 *
+	 * (In particular, allocating the IO range for Cardbus)
+	 */
+	request_region(pr->throttling.address, 6, "ACPI CPU throttle");
+
 	pr->throttling.state = 0;
 
 	duty_mask = pr->throttling.state_count - 1;