linux-kernel - [PATCH v2] x86: honor ACPI FADT flag indicating absence of a CMOS RTC

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Message-Id: <5265029D02000078000FC4D2@nat28.tlf.novell.com>
Date:	Mon, 21 Oct 2013 09:31:57 +0100
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Ingo Molnar" <mingo@...nel.org>, <tglx@...utronix.de>,
	<hpa@...or.com>
Cc:	"John Stultz" <john.stultz@...aro.org>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH v2] x86: 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@...e.com>
---
v2: Emit a log message in this case, as requested by Ingo.
---
 arch/x86/kernel/rtc.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- 3.12-rc6/arch/x86/kernel/rtc.c
+++ 3.12-rc6-x86-ACPI-no-RTC/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");



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