x86/acpi, x86/boot: Take RSDP address for boot params if available

In case the RSDP address in struct boot_params is specified don't try
to find the table by searching, but take the address directly as set
by the boot loader.

Signed-off-by: Juergen Gross <jgross@suse.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Jia Zhang <qianyue.zj@alibaba-inc.com>
Cc: Len Brown <len.brown@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Pavel Tatashin <pasha.tatashin@oracle.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: boris.ostrovsky@oracle.com
Cc: linux-kernel@vger.kernel.org
Cc: linux-pm@vger.kernel.org
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/20181010061456.22238-4-jgross@suse.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/include/asm/acpi.h b/arch/x86/include/asm/acpi.h
index a303d7b..2f01eb4 100644
--- a/arch/x86/include/asm/acpi.h
+++ b/arch/x86/include/asm/acpi.h
@@ -142,6 +142,8 @@ static inline u64 acpi_arch_get_root_pointer(void)
 
 void acpi_generic_reduced_hw_init(void);
 
+u64 x86_default_get_root_pointer(void);
+
 #else /* !CONFIG_ACPI */
 
 #define acpi_lapic 0
@@ -153,6 +155,11 @@ static inline void disable_acpi(void) { }
 
 static inline void acpi_generic_reduced_hw_init(void) { }
 
+static inline u64 x86_default_get_root_pointer(void)
+{
+	return 0;
+}
+
 #endif /* !CONFIG_ACPI */
 
 #define ARCH_HAS_POWER_INIT	1