[Patch] acpi: introduce "acpi_addr=" parameter for kdump

[Amerigo Wang <amwang@redhat.com>]

From: Takao Indoh <tindoh@redhat.com>

There is a problem with putting the first kernel in EFI virtual mode,
it is that when the second kernel comes up it tries to initialize the
EFI again and once we have put EFI in virtual mode we can not really
do that.

Actually, EFI is not necessary for kdump, we can boot the second kernel
with "noefi" parameter, but the boot will mostly fail because 2nd kernel
cannot find RSDP.

In this situation, we introduced "acpi_addr=" kernel parameter,
so that kexec-tools can pass the "noefi acpi_addr=X" to the second kernel
to make kdump works.

Signed-off-by: Takao Indoh <tindoh@redhat.com>
[amwang@redhat.com: Add documentation.]
Signed-off-by: WANG Cong <amwang@redhat.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Vivek Goyal <vgoyal@redhat.com>

---

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index f4a04c0..0fbbdc6 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -163,6 +163,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 
 			See also Documentation/power/pm.txt, pci=noacpi
 
+	acpi_addr=	[ACPI,EFI]
+			Pass the RSDP address to the kernel, mostly used
+			on machines running EFI runtime service to boot the
+			second kernel for kdump.
+
 	acpi_apic_instance=	[ACPI, IOAPIC]
 			Format: <int>
 			2: use 2nd APIC table, if available
diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
index c90c76a..06dfec0 100644
--- a/drivers/acpi/osl.c
+++ b/drivers/acpi/osl.c
@@ -238,8 +238,19 @@ void acpi_os_vprintf(const char *fmt, va_list args)
 #endif
 }
 
+static unsigned long acpi_addr;
+static int __init setup_acpi_addr(char *arg)
+{
+	acpi_addr = simple_strtoul(arg, NULL, 16);
+	return 0;
+}
+early_param("acpi_addr", setup_acpi_addr);
+
 acpi_physical_address __init acpi_os_get_root_pointer(void)
 {
+	if (acpi_addr)
+		return acpi_addr;
+
 	if (efi_enabled) {
 		if (efi.acpi20 != EFI_INVALID_TABLE_ADDR)
 			return efi.acpi20;