ACPI: Add CMOS RTC Operation Region handler support

On HP Folio 13-2000, the BIOS defines a CMOS RTC Operation Region and
the EC's _REG methord accesses that region.  Thus an appropriate
address space handler must be registered for that region before the
EC driver is loaded.

Introduce a mechanism for adding CMOS RTC address space handlers.
Register an ACPI scan handler for CMOS RTC devices such that, when
a device of that kind is detected during an ACPI namespace scan, a
common CMOS RTC operation region address space handler will be
installed for it.

References: https://bugzilla.kernel.org/show_bug.cgi?id=54621
Reported-and-tested-by: Stefan Nagy <public@stefan-nagy.at>
Signed-off-by: Lan Tianyu <tianyu.lan@intel.com>
Cc: 3.9+ <stable@vger.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/Makefile

@@ -43,6 +43,7 @@ acpi-y				+= acpi_platform.o
 acpi-y				+= power.o
 acpi-y				+= event.o
 acpi-y				+= sysfs.o
+acpi-$(CONFIG_X86)		+= acpi_cmos_rtc.o
 acpi-$(CONFIG_DEBUG_FS)		+= debugfs.o
 acpi-$(CONFIG_ACPI_NUMA)	+= numa.o
 acpi-$(CONFIG_ACPI_PROCFS_POWER) += cm_sbs.o

drivers/acpi/acpi_cmos_rtc.c

@@ -0,0 +1,92 @@
+/*
+ * ACPI support for CMOS RTC Address Space access
+ *
+ * Copyright (C) 2013, Intel Corporation
+ * Authors: Lan Tianyu <tianyu.lan@intel.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/acpi.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <asm-generic/rtc.h>
+
+#include "internal.h"
+
+#define PREFIX "ACPI: "
+
+ACPI_MODULE_NAME("cmos rtc");
+
+static const struct acpi_device_id acpi_cmos_rtc_ids[] = {
+	{ "PNP0B00" },
+	{ "PNP0B01" },
+	{ "PNP0B02" },
+	{}
+};
+
+static acpi_status
+acpi_cmos_rtc_space_handler(u32 function, acpi_physical_address address,
+		      u32 bits, u64 *value64,
+		      void *handler_context, void *region_context)
+{
+	int i;
+	u8 *value = (u8 *)&value64;
+
+	if (address > 0xff || !value64)
+		return AE_BAD_PARAMETER;
+
+	if (function != ACPI_WRITE && function != ACPI_READ)
+		return AE_BAD_PARAMETER;
+
+	spin_lock_irq(&rtc_lock);
+
+	for (i = 0; i < DIV_ROUND_UP(bits, 8); ++i, ++address, ++value)
+		if (function == ACPI_READ)
+			*value = CMOS_READ(address);
+		else
+			CMOS_WRITE(*value, address);
+
+	spin_unlock_irq(&rtc_lock);
+
+	return AE_OK;
+}
+
+static int acpi_install_cmos_rtc_space_handler(struct acpi_device *adev,
+		const struct acpi_device_id *id)
+{
+	acpi_status status;
+
+	status = acpi_install_address_space_handler(adev->handle,
+			ACPI_ADR_SPACE_CMOS,
+			&acpi_cmos_rtc_space_handler,
+			NULL, NULL);
+	if (ACPI_FAILURE(status)) {
+		pr_err(PREFIX "Error installing CMOS-RTC region handler\n");
+		return -ENODEV;
+	}
+
+	return 0;
+}
+
+static void acpi_remove_cmos_rtc_space_handler(struct acpi_device *adev)
+{
+	if (ACPI_FAILURE(acpi_remove_address_space_handler(adev->handle,
+			ACPI_ADR_SPACE_CMOS, &acpi_cmos_rtc_space_handler)))
+		pr_err(PREFIX "Error removing CMOS-RTC region handler\n");
+}
+
+static struct acpi_scan_handler cmos_rtc_handler = {
+	.ids = acpi_cmos_rtc_ids,
+	.attach = acpi_install_cmos_rtc_space_handler,
+	.detach = acpi_remove_cmos_rtc_space_handler,
+};
+
+void __init acpi_cmos_rtc_init(void)
+{
+	acpi_scan_add_handler(&cmos_rtc_handler);
+}

drivers/acpi/internal.h

@@ -45,6 +45,11 @@ void acpi_memory_hotplug_init(void);
 #else
 static inline void acpi_memory_hotplug_init(void) {}
 #endif
+#ifdef CONFIG_X86
+void acpi_cmos_rtc_init(void);
+#else
+static inline void acpi_cmos_rtc_init(void) {}
+#endif
 
 void acpi_sysfs_add_hotplug_profile(struct acpi_hotplug_profile *hotplug,
 				    const char *name);

drivers/acpi/scan.c

@@ -2040,6 +2040,7 @@ int __init acpi_scan_init(void)
 	acpi_pci_link_init();
 	acpi_platform_init();
 	acpi_lpss_init();
+	acpi_cmos_rtc_init();
 	acpi_container_init();
 	acpi_memory_hotplug_init();