From: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>

Make the CMOS RTC ACPI scan handler create a platform device that will
be used subsequently by rtc-cmos for driver binding on x86 systems with
ACPI and update add_rtc_cmos() to skip registering a fallback platform
device for the CMOS RTC when the above one has been registered.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 arch/x86/kernel/rtc.c       | 4 ++++
 drivers/acpi/x86/cmos_rtc.c | 8 ++++++++
 include/linux/acpi.h        | 4 ++++
 3 files changed, 16 insertions(+)

diff --git a/arch/x86/kernel/rtc.c b/arch/x86/kernel/rtc.c
index 51a849a79c98..b112178e8185 100644
--- a/arch/x86/kernel/rtc.c
+++ b/arch/x86/kernel/rtc.c
@@ -2,6 +2,7 @@
 /*
  * RTC related functions
  */
+#include <linux/acpi.h>
 #include <linux/platform_device.h>
 #include <linux/mc146818rtc.h>
 #include <linux/export.h>
@@ -146,6 +147,9 @@ static __init int add_rtc_cmos(void)
 		}
 	}
 #endif
+	if (cmos_rtc_platform_device_present)
+		return 0;
+
 	if (!x86_platform.legacy.rtc)
 		return -ENODEV;
 
diff --git a/drivers/acpi/x86/cmos_rtc.c b/drivers/acpi/x86/cmos_rtc.c
index 45db7e51cbe6..bdd66dfd4a44 100644
--- a/drivers/acpi/x86/cmos_rtc.c
+++ b/drivers/acpi/x86/cmos_rtc.c
@@ -24,6 +24,8 @@ static const struct acpi_device_id acpi_cmos_rtc_ids[] = {
 	{}
 };
 
+bool cmos_rtc_platform_device_present;
+
 static bool cmos_rtc_space_handler_present __read_mostly;
 
 static acpi_status acpi_cmos_rtc_space_handler(u32 function,
@@ -103,6 +105,12 @@ static int acpi_cmos_rtc_attach(struct acpi_device *adev,
 	if (ret < 0)
 		return ret;
 
+	if (IS_ERR_OR_NULL(acpi_create_platform_device(adev, NULL))) {
+		pr_err("Failed to create CMOS-RTC platform device\n");
+		return 0;
+	} else {
+		cmos_rtc_platform_device_present = true;
+	}
 	return 1;
 }
 
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 4d2f0bed7a06..2bdb801cee01 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -791,6 +791,8 @@ const char *acpi_get_subsystem_id(acpi_handle handle);
 int acpi_mrrm_max_mem_region(void);
 #endif
 
+extern bool cmos_rtc_platform_device_present;
+
 #else	/* !CONFIG_ACPI */
 
 #define acpi_disabled 1
@@ -1116,6 +1118,8 @@ static inline int acpi_mrrm_max_mem_region(void)
 	return 1;
 }
 
+#define cmos_rtc_platform_device_present	false
+
 #endif	/* !CONFIG_ACPI */
 
 #ifdef CONFIG_ACPI_HMAT
-- 
2.51.0

On 2/23/26 07:29, Rafael J. Wysocki wrote:
> Make the CMOS RTC ACPI scan handler create a platform device that will
> be used subsequently by rtc-cmos for driver binding on x86 systems with
> ACPI and update add_rtc_cmos() to skip registering a fallback platform
> device for the CMOS RTC when the above one has been registered.

Acked-by: Dave Hansen <dave.hansen@linux.intel.com> # x86