[PATCH RFC 0/3] alarmtimer: Choose the wakeup RTC per sleep state from the device tree

[Neil Armstrong]

On 11/4/26 06:54, Igor Velkov via B4 Relay wrote:
> alarmtimer binds to the first registered RTC that has an alarm and a
> wakeup-capable parent and programs it on every suspend. On ODROID-HC4
> that RTC is amlogic,meson-vrtc: a register the SoC firmware reads when
> the application processors suspend. It wakes the board from deep sleep
> only, and only when the firmware handles the alarm; it raises no
> interrupt in Linux, so it never wakes the board from s2idle. The board's
> pcf8563, whose interrupt line goes to a GPIO, registers later and is
> never used.
> 
> Which RTC wakes the system depends on the sleep state and on the board's
> firmware, so the series lets the board device tree say it per RTC:
> 
> - linux,wakeup-states: the sleep states an alarm of this RTC wakes the
>    system from ("s2idle", "shallow", "deep" as in /sys/power/mem_sleep,
>    plus "hibernate" and "off"), or "none".
> - linux,alarmtimer-priority: a weight to pick among several RTCs that
>    wake the system from the same state.

This sounds bulky, perhaps it would be much simpler if we just added
all the available RTCs which has RTC_FEATURE_ALARM and can wakeup ?

Just switch from 1 single to multiple RTCs in a linked list and you're
done, no DT & bindings changes.

Neil

> 
> alarmtimer keeps each RTC that has an alarm and a wakeup-capable parent,
> unless an RTC registered before it, with at least the same priority,
> already wakes from every state it lists; each kept RTC gets its own
> "alarmtimer" platform device under the RTC. alarmtimer_suspend() picks,
> by pm_suspend_target_state, the RTC with the highest priority among
> those listing that state, the first registered among equals, and
> programs the alarm from that RTC's platform device only. The driver core
> suspends a device before its ancestors (dpm_suspend() takes
> dpm_prepared_list from the tail, in reverse registration order), so the
> chosen RTC and its parent, which drives the hardware, are still awake
> when the alarm is programmed.
> Without the properties only the first RTC gets a platform device and
> alarmtimer programs it on every suspend.
> 
> An RTC without linux,wakeup-states is taken to wake the system from
> every state, so that adding the property to one RTC, e.g. from an
> overlay, does not change how the others are used; a priority on the new
> one settles which wins.
> 
> Hibernation wakeups (.freeze/.poweroff callbacks) are not part of this
> series.
> 
> Patch 3 sets linux,wakeup-states on ODROID-HC4: "s2idle" for the
> pcf8563 and "deep" for meson-vrtc, so that alarmtimer programs the
> pcf8563 for s2idle and meson-vrtc for deep sleep. The patch applies to
> the current tree, but the s2idle wakeup also needs the pcf8563
> interrupt (GPIOX_5), which a patch under review adds [1].
> 
> Tested on ODROID-HC4 with v7.3.1, [1] and a BL301 that handles the vrtc
> alarm, waking by a CLOCK_BOOTTIME_ALARM timer, once per state: s2idle
> woke on the pcf8563 interrupt, deep sleep on meson-vrtc with the pcf8563
> alarm left unset. Without the series the alarm went to meson-vrtc and
> the board did not wake from s2idle.
> 
> Questions:
> 
> - Are "linux,wakeup-states" and "linux,alarmtimer-priority" acceptable
>    names, or should they be generic (no linux, prefix), given that the
>    states describe the hardware and the firmware rather than Linux?
> - Is the device tree the right place for a capability that depends on
>    the firmware the board runs? On HC4, meson-vrtc wakes from deep sleep
>    only with a BL301 that handles its alarm.
> 
> The alarm limit of meson-vrtc also depends on the firmware, and the
> kernel cannot learn it. Some API is needed to pass this information to
> the kernel.
> 
> [1] https://lore.kernel.org/r/20261020-hc4-rtc-alarm-irq-v1-1-b2b8c68d54f5@iav.lv
> 
> Signed-off-by: Igor Velkov <iav at iav.lv>
> ---
> Igor Velkov (3):
>        dt-bindings: rtc: Add linux,wakeup-states and linux,alarmtimer-priority
>        alarmtimer: Choose the wakeup RTC by sleep state and priority
>        arm64: dts: amlogic: meson-sm1-odroid-hc4: Describe which RTC wakes the board
> 
>   .../bindings/rtc/amlogic,meson-vrtc.yaml           |   3 +
>   .../devicetree/bindings/rtc/nxp,pcf8563.yaml       |   3 +
>   Documentation/devicetree/bindings/rtc/rtc.yaml     |  29 ++++
>   .../boot/dts/amlogic/meson-sm1-odroid-hc4.dts      |   5 +
>   kernel/time/alarmtimer.c                           | 157 ++++++++++++++++++---
>   5 files changed, 180 insertions(+), 17 deletions(-)
> ---
> base-commit: 348f54c435bf3177baa78201952810b255d44b30
> change-id: 20261104-b4-alarmtimer-rtc-priority-2e25131a2917
> 
> Best regards,