ibft: Fix finding IBFT ACPI table on UEFI

Found one system with UEFI/iBFT, kernel does not detect the iBFT during
iscsi_ibft module loading.

Root cause: on x86 (UEFI), we are calling of find_ibft_region() much earlier
- specifically in setup_arch() before ACPI is enabled.

Try to split acpi checking code out and call that later

At that time ACPI iBFT already get permanent mapped with ioremap.
So isa_virt_to_bus() will get wrong phys from right virt address.
We could just skip that phys address printing.

For legacy one, print the found address early.

-v2: update comments and description according to Konrad.
-v3: fix problem about module use case that is found by Konrad.
-v4: use acpi_get_table() instead of acpi_table_parse() to handle module use case that is found by Konrad again..
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Konrad Rzeszutek Wilk <konrad@kernel.org>

drivers/firmware/iscsi_ibft.c

@@ -746,6 +746,37 @@ static void __exit ibft_exit(void)
 	ibft_cleanup();
 }
 
+#ifdef CONFIG_ACPI
+static const struct {
+	char *sign;
+} ibft_signs[] = {
+	/*
+	 * One spec says "IBFT", the other says "iBFT". We have to check
+	 * for both.
+	 */
+	{ ACPI_SIG_IBFT },
+	{ "iBFT" },
+};
+
+static void __init acpi_find_ibft_region(void)
+{
+	int i;
+	struct acpi_table_header *table = NULL;
+
+	if (acpi_disabled)
+		return;
+
+	for (i = 0; i < ARRAY_SIZE(ibft_signs) && !ibft_addr; i++) {
+		acpi_get_table(ibft_signs[i].sign, 0, &table);
+		ibft_addr = (struct acpi_table_ibft *)table;
+	}
+}
+#else
+static void __init acpi_find_ibft_region(void)
+{
+}
+#endif
+
 /*
  * ibft_init() - creates sysfs tree entries for the iBFT data.
  */
@@ -753,9 +784,16 @@ static int __init ibft_init(void)
 {
 	int rc = 0;
 
+	/*
+	   As on UEFI systems the setup_arch()/find_ibft_region()
+	   is called before ACPI tables are parsed and it only does
+	   legacy finding.
+	*/
+	if (!ibft_addr)
+		acpi_find_ibft_region();
+
 	if (ibft_addr) {
-		printk(KERN_INFO "iBFT detected at 0x%llx.\n",
-		       (u64)isa_virt_to_bus(ibft_addr));
+		pr_info("iBFT detected.\n");
 
 		rc = ibft_check_device();
 		if (rc)