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Add alarm support, based on Section 9.17 of ACPI 6.6 [1], to the RTC class device interface of the driver. The ACPI time and alarm device (TAD) can support two separate alarm timers, one for waking up the system when it is on AC power, and one for waking it up when it is on DC power. In principle, each of them can be set to a different value representing the number of seconds till the given alarm timer expires. However, the RTC class device can only set one alarm, so it will set both the alarm timers of the ACPI TAD (if the DC one is supported) to the same value. That is somewhat cumbersome because there is no way in the ACPI TAD firmware interface to set both timers in one go, so they need to be set sequentially, but that's how it goes. On the alarm read side, the driver assumes that both timers have been set to the same value, so it is sufficient to access one of them (the AC one specifically). Link: https://uefi.org/specs/ACPI/6.6/09_ACPI_Defined_Devices_and_Device_Specific_Objects.html#time-and-alarm-device [1] Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com> Link: https://patch.msgid.link/2076980.usQuhbGJ8B@rafael.j.wysocki
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. 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