rtc: meson-vrtc: Use ktime_get_real_ts64() to get the current time

The VRTC alarm register can be programmed with an amount of seconds
after which the SoC will be woken up by the VRTC timer again. We are
already converting the alarm time from meson_vrtc_set_alarm() to
"seconds since 1970". This means we also need to use "seconds since
1970" for the current time.

This fixes a problem where setting the alarm to one minute in the future
results in the firmware (which handles wakeup) to output (on the serial
console) that the system will be woken up in billions of seconds.
ktime_get_raw_ts64() returns the time since boot, not since 1970. Switch
to ktime_get_real_ts64() to fix the calculation of the alarm time and to
make the SoC wake up at the specified date/time. Also the firmware
(which manages suspend) now prints either 59 or 60 seconds until wakeup
(depending on how long it takes for the system to enter suspend).

Fixes: 6ef35398e827 ("rtc: Add Amlogic Virtual Wake RTC")
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Link: https://lore.kernel.org/r/20230320212142.2355062-1-martin.blumenstingl@googlemail.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

rtc: rework rtc_register_device() resource management

rtc_register_device() is a managed interface but it doesn't use devres
by itself - instead it marks an rtc_device as "registered" and the devres
callback for devm_rtc_allocate_device() takes care of resource release.

This doesn't correspond with the design behind devres where managed
structures should not be aware of being managed. The correct solution
here is to register a separate devres callback for unregistering the
device.

While at it: rename rtc_register_device() to devm_rtc_register_device()
and add it to the list of managed interfaces in devres.rst. This way we
can avoid any potential confusion of driver developers who may expect
there to exist a corresponding unregister function.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20201109163409.24301-8-brgl@bgdev.pl

rtc: meson: simplify the return expression of meson_vrtc_probe

Simplify the return expression.

Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Acked-by: Kevin Hilman <khilman@baylibre.com>
Link: https://lore.kernel.org/r/20200919100856.1639319-1-liushixin2@huawei.com

rtc: meson: mark PM functions as __maybe_unused

The meson_vrtc_set_wakeup_time() function is only used by
the PM functions and causes a warning when they are disabled:

drivers/rtc/rtc-meson-vrtc.c:32:13: error: unused function 'meson_vrtc_set_wakeup_time' [-Werror,-Wunused-function]

Remove the #ifdef around the callers and add a __maybe_unused
annotation as a more reliable way to avoid these warnings.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Link: https://lore.kernel.org/r/20190906152438.1533833-1-arnd@arndb.de
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

rtc: Add Amlogic Virtual Wake RTC

The Amlogic Meson GX SoCs uses a special register to store the
time in seconds to wakeup after a system suspend.

In order to be able to reuse the RTC wakealarm feature, this
driver implements a fake RTC device which uses the system time
to deduce a suspend delay.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
[khilman: rebase to v5.3-rc, rework and modernization]
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Link: https://lore.kernel.org/r/20190812232850.8016-3-khilman@kernel.org
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>