rtc: opal: switch to RTC_FEATURE_UPDATE_INTERRUPT

Stop using uie_unsupported and clear RTC_FEATURE_UPDATE_INTERRUPT instead.

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

rtc: opal: switch to RTC_FEATURE_UPDATE_INTERRUPT

Stop using uie_unsupported and clear RTC_FEATURE_UPDATE_INTERRUPT instead.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220309162301.61679-7-alexandre.belloni@bootlin.com

show more ...

rtc: opal: constify opal_rtc_ops

Use RTC_FEATURE_ALARM to signal to the core whether alarms are available
instead of changing the global struct rtc_class_ops, allowing to make it
const.

Signed-off-

rtc: opal: constify opal_rtc_ops

Use RTC_FEATURE_ALARM to signal to the core whether alarms are available
instead of changing the global struct rtc_class_ops, allowing to make it
const.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20210110231752.1418816-13-alexandre.belloni@bootlin.com

show more ...

rtc: opal: set range

It is a BCD RTC with 4 digits for the year.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20210110224606.1414307-1-alexandre.

rtc: opal: set range

It is a BCD RTC with 4 digits for the year.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20210110224606.1414307-1-alexandre.belloni@bootlin.com

show more ...

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 114

Based on 1 normalized pattern(s):

this program is free software you can redistribute it and or modify
it under the terms of th

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 114

Based on 1 normalized pattern(s):

this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation either version 2 of the license or at
your option any later version this program is distributed in the
hope that it will be useful but without any warranty without even
the implied warranty of merchantability or fitness for a particular
purpose see the gnu general public license for more details you
should have received a copy of the gnu general public license along
with this program

extracted by the scancode license scanner the SPDX license identifier

GPL-2.0-or-later

has been chosen to replace the boilerplate/reference in 8 file(s).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Reviewed-by: Richard Fontana <rfontana@redhat.com>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190523091650.663497195@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

show more ...

rtc: opal: Make opal_tpo_alarm_irq_enable static

Fix sparse warning:

drivers/rtc/rtc-opal.c:227:5:
warning: symbol 'opal_tpo_alarm_irq_enable' was not declared. Should it be static?

Signed-off-by

rtc: opal: Make opal_tpo_alarm_irq_enable static

Fix sparse warning:

drivers/rtc/rtc-opal.c:227:5:
warning: symbol 'opal_tpo_alarm_irq_enable' was not declared. Should it be static?

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

show more ...

rtc: opal: Fix OPAL RTC driver OPAL_BUSY loops

The OPAL RTC driver does not sleep in case it gets OPAL_BUSY or
OPAL_BUSY_EVENT from firmware, which causes large scheduling
latencies, up to 50 second

rtc: opal: Fix OPAL RTC driver OPAL_BUSY loops

The OPAL RTC driver does not sleep in case it gets OPAL_BUSY or
OPAL_BUSY_EVENT from firmware, which causes large scheduling
latencies, up to 50 seconds have been observed here when RTC stops
responding (BMC reboot can do it).

Fix this by converting it to the standard form OPAL_BUSY loop that
sleeps.

Fixes: 628daa8d5abf ("powerpc/powernv: Add RTC and NVRAM support plus RTAS fallbacks")
Cc: stable@vger.kernel.org # v3.2+
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

show more ...

rtc-opal: Fix handling of firmware error codes, prevent busy loops

According to the OPAL docs:
skiboot-5.2.5/doc/opal-api/opal-rtc-read-3.txt
skiboot-5.2.5/doc/opal-api/opal-rtc-write-4.txt

OPA

rtc-opal: Fix handling of firmware error codes, prevent busy loops

According to the OPAL docs:
skiboot-5.2.5/doc/opal-api/opal-rtc-read-3.txt
skiboot-5.2.5/doc/opal-api/opal-rtc-write-4.txt

OPAL_HARDWARE may be returned from OPAL_RTC_READ or OPAL_RTC_WRITE and
this indicates either a transient or permanent error.

Prior to this patch, Linux was not dealing with OPAL_HARDWARE being a
permanent error particularly well, in that you could end up in a busy
loop.

This was not too hard to trigger on an AMI BMC based OpenPOWER machine
doing a continuous "ipmitool mc reset cold" to the BMC, the result of
that being that we'd get stuck in an infinite loop in
opal_get_rtc_time().

We now retry a few times before returning the error higher up the
stack.

Fixes: 16b1d26e77b1 ("rtc/tpo: Driver to support rtc and wakeup on PowerNV platform")
Cc: stable@vger.kernel.org # v3.19+
Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

show more ...

rtc: opal: Implement rtc_class_ops.alarm_irq_enable callback

Provide an implementation of the callback
rtc_class_ops.alarm_irq_enable for rtc-opal driver. This callback is
called when the wake alarm

rtc: opal: Implement rtc_class_ops.alarm_irq_enable callback

Provide an implementation of the callback
rtc_class_ops.alarm_irq_enable for rtc-opal driver. This callback is
called when the wake alarm is disabled via the command:

'echo 0 > /sys/class/rtc/rtc0/wakealarm'

Without this the Timed-Power-On(TPO) config remains set even when its
disabled by the above command and FSP will still force machine
boot at previously configured alarm time.

The callback is implemented as function opal_tpo_alarm_irq_enable()
which calls opal_set_tpo_time() with alarm.enabled == 0. A branch is
added to opal_set_tpo_time() to handle this case by passing y_m_d ==
h_m_s_ms == 0 to opal as arguments for opal_tpo_write() call.

Signed-off-by: Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

show more ...

rtc: opal: Handle disabled TPO in opal_get_tpo_time()

On PowerNV platform when Timed-Power-On(TPO) is disabled, read of
stored TPO yields value with all date components set to '0' inside
opal_get_tp

rtc: opal: Handle disabled TPO in opal_get_tpo_time()

On PowerNV platform when Timed-Power-On(TPO) is disabled, read of
stored TPO yields value with all date components set to '0' inside
opal_get_tpo_time(). The function opal_to_tm() then converts it to an
offset from year 1900 yielding alarm-time == "1900-00-01
00:00:00". This causes problems with __rtc_read_alarm() that
expecting an offset from "1970-00-01 00:00:00" and returned alarm-time
results in a -ve value for time64_t. Which ultimately results in this
error reported in kernel logs with a seemingly garbage value:

"rtc rtc0: invalid alarm value: -2-1--1041528741
2005511117:71582844:32"

We fix this by explicitly handling the case of all alarm date-time
components being '0' inside opal_get_tpo_time() and returning -ENOENT
in such a case. This signals generic rtc that no alarm is set and it
bails out from the alarm initialization flow without reporting the
above error.

Signed-off-by: Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
Reported-by: Steve Best <sbest@redhat.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

show more ...

powerpc/opal: Add inline function to get rc from an ASYNC_COMP opal_msg

An opal_msg of type OPAL_MSG_ASYNC_COMP contains the return code in the
params[1] struct member. However this isn't intuitive

powerpc/opal: Add inline function to get rc from an ASYNC_COMP opal_msg

An opal_msg of type OPAL_MSG_ASYNC_COMP contains the return code in the
params[1] struct member. However this isn't intuitive or obvious when
reading the code and requires that a user look at the skiboot
documentation or opal-api.h to verify this.

Add an inline function to get the return code from an opal_msg and update
call sites accordingly.

Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

show more ...

powerpc: Remove broken GregorianDay()

GregorianDay() is supposed to calculate the day of the week
(tm->tm_wday) for a given day/month/year. In that calcuation it
indexed into an array called MonthOf

powerpc: Remove broken GregorianDay()

GregorianDay() is supposed to calculate the day of the week
(tm->tm_wday) for a given day/month/year. In that calcuation it
indexed into an array called MonthOffset using tm->tm_mon-1. However
tm_mon is zero-based, not one-based, so this is off-by-one. It also
means that every January, GregoiranDay() will access element -1 of
the MonthOffset array.

It also doesn't appear to be a correct algorithm either: see in
contrast kernel/time/timeconv.c's time_to_tm function.

It's been broken forever, which suggests no-one in userland uses
this. It looks like no-one in the kernel uses tm->tm_wday either
(see e.g. drivers/rtc/rtc-ds1305.c:319).

tm->tm_wday is conventionally set to -1 when not available in
hardware so we can simply set it to -1 and drop the function.
(There are over a dozen other drivers in drivers/rtc that do
this.)

Found using UBSAN.

Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Andrew Morton <akpm@linux-foundation.org> # as an example of what UBSan finds.
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Cc: rtc-linux@googlegroups.com
Signed-off-by: Daniel Axtens <dja@axtens.net>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

show more ...

rtc: opal: enable support for the stardard "wakeup-source" property

Though the opal rtc driver should and will continue to support the legacy
"has-tpo" property to enable RTC as the wakeup source, w

rtc: opal: enable support for the stardard "wakeup-source" property

Though the opal rtc driver should and will continue to support the legacy
"has-tpo" property to enable RTC as the wakeup source, we need to add
support for the new standard property "wakeup-source"

This patch adds support for "wakeup-source" property in addition to the
existing "has-tpo" property.

Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Cc: rtc-linux@googlegroups.com
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

show more ...

rtc: opal: fix type of token

The variable can take signed values.

The problem has been detected using proposed semantic patch
scripts/coccinelle/tests/unsigned_lesser_than_zero.cocci [1].

[1]: htt

rtc: opal: fix type of token

The variable can take signed values.

The problem has been detected using proposed semantic patch
scripts/coccinelle/tests/unsigned_lesser_than_zero.cocci [1].

[1]: http://permalink.gmane.org/gmane.linux.kernel/2038576

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

show more ...

rtc: opal: Enable alarms only when opal supports tpo

rtc-opal driver provides support for rtc alarms via
timed-power-on(tpo). However some Power platforms like BML use a fake
rtc clock and don't sup

rtc: opal: Enable alarms only when opal supports tpo

rtc-opal driver provides support for rtc alarms via
timed-power-on(tpo). However some Power platforms like BML use a fake
rtc clock and don't support tpo. Such platforms are indicated by the
missing 'has-tpo' property in the device tree.

Current implementation however enables callback for
rtc_class_ops.read/set alarm irrespective of the tpo support from the
platform. This results in a failed opal call when kernel tries to read
an existing alarms via opal_get_tpo_time during rtc device registration.

This patch fixes this issue by setting opal_rtc_ops.read/set_alarm
callback pointers only when tpo is supported.

Acked-by: Michael Neuling <mikey@neuling.org>
Acked-by: Neelesh Gupta <neelegup@linux.vnet.ibm.com>
Signed-off-by: Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
Acked-by: Stewart Smith <stewart@linux.vnet.ibm.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

show more ...

rtc: Drop owner assignment from platform_driver

platform_driver does not need to set an owner because
platform_driver_register() will set it.

Signed-off-by: Alexandre Belloni <alexandre.belloni@fre

rtc: Drop owner assignment from platform_driver

platform_driver does not need to set an owner because
platform_driver_register() will set it.

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

show more ...

rtc: use more standard kernel logging styles

Neaten the logging a bit by adding #define pr_fmt

Miscellanea:

o Remove __FILE__/__func__ uses
o Coalesce formats adding missing spaces
o Align argumen

rtc: use more standard kernel logging styles

Neaten the logging a bit by adding #define pr_fmt

Miscellanea:

o Remove __FILE__/__func__ uses
o Coalesce formats adding missing spaces
o Align arguments
o (rtc-cmos) Integrated 2 consecutive messages

Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Joshua Kinard <kumba@gentoo.org>
Cc: Chanwoo Choi <cw00.choi@samsung.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Tested-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Cc: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

show more ...

rtc/tpo: Driver to support rtc and wakeup on PowerNV platform

The patch implements the OPAL rtc driver that binds with the rtc
driver subsystem. The driver uses the platform device infrastructure
to

rtc/tpo: Driver to support rtc and wakeup on PowerNV platform

The patch implements the OPAL rtc driver that binds with the rtc
driver subsystem. The driver uses the platform device infrastructure
to probe the rtc device and register it to rtc class framework. The
'wakeup' is supported depending upon the property 'has-tpo' present
in the OF node. It provides a way to load the generic rtc driver in
in the absence of an OPAL driver.

The patch also moves the existing OPAL rtc get/set time interfaces to the
new driver and exposes the necessary OPAL calls using EXPORT_SYMBOL_GPL.

Test results:
-------------
Host:
[root@tul169p1 ~]# ls -l /sys/class/rtc/
total 0
lrwxrwxrwx 1 root root 0 Oct 14 03:07 rtc0 -> ../../devices/opal-rtc/rtc/rtc0
[root@tul169p1 ~]# cat /sys/devices/opal-rtc/rtc/rtc0/time
08:10:07
[root@tul169p1 ~]# echo `date '+%s' -d '+ 2 minutes'` > /sys/class/rtc/rtc0/wakealarm
[root@tul169p1 ~]# cat /sys/class/rtc/rtc0/wakealarm
1413274345
[root@tul169p1 ~]#

FSP:
$ smgr mfgState
standby
$ rtim timeofday

System time is valid: 2014/10/14 08:12:04.225115

$ smgr mfgState
ipling
$

CC: devicetree@vger.kernel.org
CC: tglx@linutronix.de
CC: rtc-linux@googlegroups.com
CC: a.zummo@towertech.it
Signed-off-by: Neelesh Gupta <neelegup@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

show more ...

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 114

Based on 1 normalized pattern(s):

this program is free software you can redistribute it and or modify
it u

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 114

Based on 1 normalized pattern(s):

this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation either version 2 of the license or at
your option any later version this program is distributed in the
hope that it will be useful but without any warranty without even
the implied warranty of merchantability or fitness for a particular
purpose see the gnu general public license for more details you
should have received a copy of the gnu general public license along
with this program

extracted by the scancode license scanner the SPDX license identifier

GPL-2.0-or-later

has been chosen to replace the boilerplate/reference in 8 file(s).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Reviewed-by: Richard Fontana <rfontana@redhat.com>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190523091650.663497195@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

show more ...

rtc: opal: Make opal_tpo_alarm_irq_enable static

Fix sparse warning:

drivers/rtc/rtc-opal.c:227:5:
warning: symbol 'opal_tpo_alarm_irq_enable' was not declared. Should it be st

rtc: opal: Make opal_tpo_alarm_irq_enable static

Fix sparse warning:

drivers/rtc/rtc-opal.c:227:5:
warning: symbol 'opal_tpo_alarm_irq_enable' was not declared. Should it be static?

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

show more ...

rtc: opal: Fix OPAL RTC driver OPAL_BUSY loops

The OPAL RTC driver does not sleep in case it gets OPAL_BUSY or
OPAL_BUSY_EVENT from firmware, which causes large scheduling
latencies,

rtc: opal: Fix OPAL RTC driver OPAL_BUSY loops

The OPAL RTC driver does not sleep in case it gets OPAL_BUSY or
OPAL_BUSY_EVENT from firmware, which causes large scheduling
latencies, up to 50 seconds have been observed here when RTC stops
responding (BMC reboot can do it).

Fix this by converting it to the standard form OPAL_BUSY loop that
sleeps.

Fixes: 628daa8d5abf ("powerpc/powernv: Add RTC and NVRAM support plus RTAS fallbacks")
Cc: stable@vger.kernel.org # v3.2+
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

show more ...

rtc-opal: Fix handling of firmware error codes, prevent busy loops

According to the OPAL docs:
skiboot-5.2.5/doc/opal-api/opal-rtc-read-3.txt
skiboot-5.2.5/doc/opal-api/opal-rtc-

rtc-opal: Fix handling of firmware error codes, prevent busy loops

According to the OPAL docs:
skiboot-5.2.5/doc/opal-api/opal-rtc-read-3.txt
skiboot-5.2.5/doc/opal-api/opal-rtc-write-4.txt

OPAL_HARDWARE may be returned from OPAL_RTC_READ or OPAL_RTC_WRITE and
this indicates either a transient or permanent error.

Prior to this patch, Linux was not dealing with OPAL_HARDWARE being a
permanent error particularly well, in that you could end up in a busy
loop.

This was not too hard to trigger on an AMI BMC based OpenPOWER machine
doing a continuous "ipmitool mc reset cold" to the BMC, the result of
that being that we'd get stuck in an infinite loop in
opal_get_rtc_time().

We now retry a few times before returning the error higher up the
stack.

Fixes: 16b1d26e77b1 ("rtc/tpo: Driver to support rtc and wakeup on PowerNV platform")
Cc: stable@vger.kernel.org # v3.19+
Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

show more ...

rtc: opal: Implement rtc_class_ops.alarm_irq_enable callback

Provide an implementation of the callback
rtc_class_ops.alarm_irq_enable for rtc-opal driver. This callback is
called whe

rtc: opal: Implement rtc_class_ops.alarm_irq_enable callback

Provide an implementation of the callback
rtc_class_ops.alarm_irq_enable for rtc-opal driver. This callback is
called when the wake alarm is disabled via the command:

'echo 0 > /sys/class/rtc/rtc0/wakealarm'

Without this the Timed-Power-On(TPO) config remains set even when its
disabled by the above command and FSP will still force machine
boot at previously configured alarm time.

The callback is implemented as function opal_tpo_alarm_irq_enable()
which calls opal_set_tpo_time() with alarm.enabled == 0. A branch is
added to opal_set_tpo_time() to handle this case by passing y_m_d ==
h_m_s_ms == 0 to opal as arguments for opal_tpo_write() call.

Signed-off-by: Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

show more ...

rtc: opal: Handle disabled TPO in opal_get_tpo_time()

On PowerNV platform when Timed-Power-On(TPO) is disabled, read of
stored TPO yields value with all date components set to '0' inside

rtc: opal: Handle disabled TPO in opal_get_tpo_time()

On PowerNV platform when Timed-Power-On(TPO) is disabled, read of
stored TPO yields value with all date components set to '0' inside
opal_get_tpo_time(). The function opal_to_tm() then converts it to an
offset from year 1900 yielding alarm-time == "1900-00-01
00:00:00". This causes problems with __rtc_read_alarm() that
expecting an offset from "1970-00-01 00:00:00" and returned alarm-time
results in a -ve value for time64_t. Which ultimately results in this
error reported in kernel logs with a seemingly garbage value:

"rtc rtc0: invalid alarm value: -2-1--1041528741
2005511117:71582844:32"

We fix this by explicitly handling the case of all alarm date-time
components being '0' inside opal_get_tpo_time() and returning -ENOENT
in such a case. This signals generic rtc that no alarm is set and it
bails out from the alarm initialization flow without reporting the
above error.

Signed-off-by: Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
Reported-by: Steve Best <sbest@redhat.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

show more ...

powerpc/opal: Add inline function to get rc from an ASYNC_COMP opal_msg

An opal_msg of type OPAL_MSG_ASYNC_COMP contains the return code in the
params[1] struct member. However this isn'

powerpc/opal: Add inline function to get rc from an ASYNC_COMP opal_msg

An opal_msg of type OPAL_MSG_ASYNC_COMP contains the return code in the
params[1] struct member. However this isn't intuitive or obvious when
reading the code and requires that a user look at the skiboot
documentation or opal-api.h to verify this.

Add an inline function to get the return code from an opal_msg and update
call sites accordingly.

Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

show more ...

powerpc: Remove broken GregorianDay()

GregorianDay() is supposed to calculate the day of the week
(tm->tm_wday) for a given day/month/year. In that calcuation it
indexed into an arra

powerpc: Remove broken GregorianDay()

GregorianDay() is supposed to calculate the day of the week
(tm->tm_wday) for a given day/month/year. In that calcuation it
indexed into an array called MonthOffset using tm->tm_mon-1. However
tm_mon is zero-based, not one-based, so this is off-by-one. It also
means that every January, GregoiranDay() will access element -1 of
the MonthOffset array.

It also doesn't appear to be a correct algorithm either: see in
contrast kernel/time/timeconv.c's time_to_tm function.

It's been broken forever, which suggests no-one in userland uses
this. It looks like no-one in the kernel uses tm->tm_wday either
(see e.g. drivers/rtc/rtc-ds1305.c:319).

tm->tm_wday is conventionally set to -1 when not available in
hardware so we can simply set it to -1 and drop the function.
(There are over a dozen other drivers in drivers/rtc that do
this.)

Found using UBSAN.

Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Andrew Morton <akpm@linux-foundation.org> # as an example of what UBSan finds.
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Cc: rtc-linux@googlegroups.com
Signed-off-by: Daniel Axtens <dja@axtens.net>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

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