rtc: add new RTC_FEATURE_ALARM_WAKEUP_ONLY feature

Some RTCs have an IRQ pin that is not connected to a CPU interrupt but
rather directly to a PMIC or power supply. In that case, it is still useful
to be able to set alarms but we shouldn't expect interrupts.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220309162301.61679-22-alexandre.belloni@bootlin.com

rtc: add BSM parameter

BSM or Backup Switch Mode is a common feature on RTCs, allowing to select
how the RTC will decide when to switch from its primary power supply to the
backup power supply. It is necessary to be able to set it from userspace as
there are uses cases where it has to be done dynamically.

Supported values are:
RTC_BSM_DISABLED: disabled
RTC_BSM_DIRECT: switching will happen as soon as Vbackup > Vdd
RTC_BSM_LEVEL: switching will happen around a threshold, usually with an
hysteresis
RTC_BSM_STANDBY: switching will not happen until Vdd > Vbackup, this is
useful to ensure the RTC doesn't draw any power until the device is first
powered on.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20211018151933.76865-6-alexandre.belloni@bootlin.com

rtc: add correction parameter

Add a new parameter allowing the get and set the correction using ioctls
instead of just sysfs.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20211018151933.76865-5-alexandre.belloni@bootlin.com

rtc: expose correction feature

Add a new feature for RTCs able to correct the oscillator imprecision. This
is also called offset or trimming. Such drivers have a .set_offset callback,
use that to set the feature bit from the core.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20211018151933.76865-4-alexandre.belloni@bootlin.com

rtc: add parameter ioctl

Add an ioctl allowing to get and set extra parameters for an RTC. For now,
only handle getting available features.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20211018151933.76865-3-alexandre.belloni@bootlin.com

rtc: add alarm related features

Add more alarm related features to be declared by drivers.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20211018151933.76865-2-alexandre.belloni@bootlin.com

rtc: introduce features bitfield

Introduce a bitfield to allow the drivers to announce the available
features for an RTC.

The main use case would be to better handle alarms, that could be present
or not or have a minute resolution or may need a correct week day to be set.

Use the newly introduced RTC_FEATURE_ALARM bit to then test whether alarms
are available instead of relying on the presence of ops->set_alarm.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20210110231752.1418816-2-alexandre.belloni@bootlin.com

rtc: add new VL flag for backup switchover

A new flag RTC_VL_BACKUP_SWITCH means that a backup switchover happened
since last flag clear.

Link: https://lore.kernel.org/r/20200505201310.255145-1-alexandre.belloni@bootlin.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

rtc: make definitions in include/uapi/linux/rtc.h actually useful for user space

BIT() macro is not defined in UAPI headers; there is, however, similarly
defined _BITUL() macro present in include/uapi/linux/const.h; use it
instead and include <linux/const.h> and <linux/ioctl.h> in order to make
the definitions provided in the header useful.

Fixes: 3431ca4837bf ("rtc: define RTC_VL_READ values")
Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
Link: https://lore.kernel.org/r/20200324041209.GA30727@asgard.redhat.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

rtc: define RTC_VL_READ values

Currently, the meaning of the value returned by RTC_VL_READ is undocumented
and left to the driver implementation. In order to get more meaningful
values, define a set of values to use as to make clear to userspace what is
the status of the various voltages feeding the RTC.

Link: https://lore.kernel.org/r/20191214220259.621996-2-alexandre.belloni@bootlin.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

License cleanup: add SPDX license identifier to uapi header files with no license

Many user space API headers are missing licensing information, which
makes it hard for compliance tools to determine the correct license.

By default are files without license information under the default
license of the kernel, which is GPLV2. Marking them GPLV2 would exclude
them from being included in non GPLV2 code, which is obviously not
intended. The user space API headers fall under the syscall exception
which is in the kernels COPYING file:

NOTE! This copyright does *not* cover user programs that use kernel
services by normal system calls - this is merely considered normal use
of the kernel, and does *not* fall under the heading of "derived work".

otherwise syscall usage would not be possible.

Update the files which contain no license information with an SPDX
license identifier. The chosen identifier is 'GPL-2.0 WITH
Linux-syscall-note' which is the officially assigned identifier for the
Linux syscall exception. SPDX license identifiers are a legally binding
shorthand, which can be used instead of the full boiler plate text.

This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne. See the previous patch in this series for the
methodology of how this patch was researched.

Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

UAPI: (Scripted) Disintegrate include/linux

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Michael Kerrisk <mtk.manpages@gmail.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Dave Jones <davej@redhat.com>