x86/time: Honor ACPI FADT flag indicating absence of a CMOS RTC

Even though the omission was found only during code review
(originally in the Xen hypervisor, looking through ACPI v5 flags
and their meanings and uses), we shouldn't be creating a
corresponding platform device in that case.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Cc: John Stultz <john.stultz@linaro.org>
Link: http://lkml.kernel.org/r/5265029D02000078000FC4D2@nat28.tlf.novell.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/rtc.c b/arch/x86/kernel/rtc.c
index 0aa29394ed6fe8dadda70aeefcf7bb2d3462e6ec..5b9dd445eb89e77654653b9e014a43ad0afd16d0 100644 (file)
--- a/arch/x86/kernel/rtc.c
+++ b/arch/x86/kernel/rtc.c
@@ -192,6 +192,14 @@ static __init int add_rtc_cmos(void)
        if (mrst_identify_cpu())
                return -ENODEV;
 
+#ifdef CONFIG_ACPI
+       if (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;
+       }
+#endif
+
        platform_device_register(&rtc_device);
        dev_info(&rtc_device.dev,
                 "registered platform RTC device (no PNP device found)\n");