rtc: Remove unused rtc_dev_exit().

Commit 270a3bd6bdc21407 ("rtc: make class.c explicitly non-modular")
removed rtc_dev_exit() call.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/1e2f9a99-435d-e149-7456-dfacd53be85a@I-love.SAKURA.ne.jp

rtc: Replace flush_scheduled_work() with flush_work().

Since "struct rtc_device" is per a device struct, I assume that clear_uie()
needs to wait for only one work associated with that device. Therefore,
wait for only that work using flush_work().

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/8d3a0f55-d861-ba93-0d25-b1172eaa8343@I-love.SAKURA.ne.jp

rtc: Move variable into switch case statement

When building with automatic stack variable initialization, GCC 12
complains about variables defined outside of switch case statements.
Move the variable into the case that uses it, which silences the warning:

drivers/rtc/dev.c: In function 'rtc_dev_ioctl':
drivers/rtc/dev.c:394:30: warning: statement will never be executed [-Wswitch-unreachable]
394 | long offset;
| ^~~~~~

Fixes: 6a8af1b6568a ("rtc: add parameter ioctl")
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20211209043915.1378393-1-keescook@chromium.org

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: 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

compat_ioctl: move rtc handling into drivers/rtc/dev.c

We no longer need the rtc compat handling to be in common code, now that
all drivers are either moved to the rtc-class framework, or (rarely)
exist in drivers/char for architectures without compat mode (m68k,
alpha and ia64, respectively).

I checked the list of ioctl commands in drivers, and the ones that are
not already handled are all compatible, again with the one exception of
m68k driver, which implements RTC_PLL_GET and RTC_PLL_SET, but has no
compat mode.

Unlike earlier versions of this patch, I'm now adding a separate
compat_ioctl handler that takes care of RTC_IRQP_READ32/RTC_IRQP_SET32
and treats all other commands as compatible, leaving the native
behavior unchanged.

The old conversion handler also deals with RTC_EPOCH_READ and
RTC_EPOCH_SET, which are not handled in rtc-dev.c but only in a single
device driver (rtc-vr41xx), so I'm adding the compat version in the same
place. I don't expect other drivers to need those commands in the future.

Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Reviewed-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
v4: handle RTC_EPOCH_SET32 in rtc_dev_compat_ioctl
v3: handle RTC_IRQP_READ32/RTC_IRQP_SET32 in rtc_dev_compat_ioctl
v2: merge compat handler into ioctl function to avoid the
compat_alloc_user_space() roundtrip, based on feedback
from Al Viro.

rtc: core: correct trivial checkpatch warnings

Correct trivial checkpatch warnings, mostly whitespace issues and
unbalanced braces.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

rtc: convert core to SPDX identifier

Use SPDX-License-Identifier instead of a verbose license text. Also fix the
block comment alignment.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

rtc: remove rtc_class_ops.read_callback

Since commit 416f0e8056f7 ("RTC: sa1100: Update the sa1100 RTC driver."),
the last user of .read_callback is gone. It has been 8 years and now new
user appeared. Simply remove it.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

rtc: rename core files

Rename core files so there is a clearer separation between the RTC core and
the RTC drivers.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>