ACPI/sleep: Convert acpi_wakeup_address into a function

Convert acpi_wakeup_address from a raw variable into a function so that
x86 can wrap its dereference of the real mode boot header in a function
instead of broadcasting it to the world via a #define.  This sets the
stage for a future patch to move x86's definition of the new function,
acpi_get_wakeup_address(), out of asm/acpi.h and thus break acpi.h's
dependency on asm/realmode.h.

No functional change intended.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Link: https://lkml.kernel.org/r/20191126165417.22423-12-sean.j.christopherson@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/ia64/include/asm/acpi.h

@@ -38,7 +38,10 @@ int acpi_gsi_to_irq (u32 gsi, unsigned int *irq);
 /* Low-level suspend routine. */
 extern int acpi_suspend_lowlevel(void);
 
-extern unsigned long acpi_wakeup_address;
+static inline unsigned long acpi_get_wakeup_address(void)
+{
+	return 0;
+}
 
 /*
  * Record the cpei override flag and current logical cpu. This is

arch/ia64/kernel/acpi.c

@@ -42,8 +42,6 @@ int acpi_lapic;
 unsigned int acpi_cpei_override;
 unsigned int acpi_cpei_phys_cpuid;
 
-unsigned long acpi_wakeup_address = 0;
-
 #define ACPI_MAX_PLATFORM_INTERRUPTS	256
 
 /* Array to record platform interrupt vectors for generic interrupt routing. */

arch/x86/include/asm/acpi.h

@@ -62,7 +62,10 @@ static inline void acpi_disable_pci(void)
 extern int (*acpi_suspend_lowlevel)(void);
 
 /* Physical address to resume after wakeup */
-#define acpi_wakeup_address ((unsigned long)(real_mode_header->wakeup_start))
+static inline unsigned long acpi_get_wakeup_address(void)
+{
+	return ((unsigned long)(real_mode_header->wakeup_start));
+}
 
 /*
  * Check if the CPU can handle C2 and deeper

drivers/acpi/sleep.c

@@ -61,8 +61,11 @@ static struct notifier_block tts_notifier = {
 static int acpi_sleep_prepare(u32 acpi_state)
 {
 #ifdef CONFIG_ACPI_SLEEP
+	unsigned long acpi_wakeup_address;
+
 	/* do we have a wakeup address for S2 and S3? */
 	if (acpi_state == ACPI_STATE_S3) {
+		acpi_wakeup_address = acpi_get_wakeup_address();
 		if (!acpi_wakeup_address)
 			return -EFAULT;
 		acpi_set_waking_vector(acpi_wakeup_address);