rtc: block registration of rtc-cmos when CMOS RTC Not Present

We should not acess CMOS address when CMOS RTC Not Present bit set in
FADT. The ee5872b patch didn't avoid rtc-cmos driver loaded when system support
ACPI PNP PNP0B0* devices.
So this patch block the registion of rtc-cmos driver to avoid
user space access RTC through CMOS interface.

Signed-off-by: Lee, Chun-Yi <jlee@suse.com>

arch/x86/kernel/rtc.c

@@ -174,16 +174,27 @@ static __init int add_rtc_cmos(void)
 	    { "PNP0b00", "PNP0b01", "PNP0b02", };
 	struct pnp_dev *dev;
 	struct pnp_id *id;
-	int i;
+	int i = 0;
+	bool found_pnp;
 
 	pnp_for_each_dev(dev) {
 		for (id = dev->id; id; id = id->next) {
 			for (i = 0; i < ARRAY_SIZE(ids); i++) {
-				if (compare_pnp_id(id, ids[i]) != 0)
-					return 0;
+				if (compare_pnp_id(id, ids[i]) != 0) {
+					found_pnp = true;
+					goto found_pnp;
+				}
 			}
 		}
 	}
+
+found_pnp:
+	if (found_pnp) {
+		if (acpi_gbl_FADT.header.revision >= 5 &&
+		    acpi_gbl_FADT.boot_flags & ACPI_FADT_NO_CMOS_RTC)
+			pr_err(FW_BUG "Found %s device but CMOS RTC Not Present flag set\n", ids[i]);
+		return 0;
+	}
 #endif
 	if (of_have_populated_dt())
 		return 0;
@@ -193,7 +204,8 @@ static __init int add_rtc_cmos(void)
 		return -ENODEV;
 
 #ifdef CONFIG_ACPI
-	if (acpi_gbl_FADT.boot_flags & ACPI_FADT_NO_CMOS_RTC) {
+	if (acpi_gbl_FADT.header.revision >= 5 &&
+	    acpi_gbl_FADT.boot_flags & ACPI_FADT_NO_CMOS_RTC) {
 		/* This warning can likely go away again in a year or two. */
 		pr_info("ACPI: not registering RTC platform device\n");
 		return -ENODEV;

drivers/rtc/rtc-cmos.c

@@ -28,6 +28,9 @@
  * interrupts disabled, holding the global rtc_lock, to exclude those
  * other drivers and utilities on correctly configured systems.
  */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/init.h>
@@ -1144,6 +1147,12 @@ static int __init cmos_init(void)
 {
 	int retval = 0;
 
+	if (acpi_gbl_FADT.header.revision >= 5 &&
+	    acpi_gbl_FADT.boot_flags & ACPI_FADT_NO_CMOS_RTC) {
+		pr_info("ACPI CMOS RTC Not Present detected - not loading\n");
+		return 0;
+	}
+
 #ifdef	CONFIG_PNP
 	retval = pnp_register_driver(&cmos_pnp_driver);
 	if (retval == 0)