linux.git/arch/x86/kernel/rtc.c, branch v7.1

x86: rtc: Drop PNP device check

2026-02-26T17:48:43+00:00

Previous changes effectively prevented PNP devices from being created
for the CMOS RTC on x86 with ACPI.

Although in principle a CMOS RTC PNP device may exist on an x86 system
without ACPI (that is, an x86 system where there is no ACPI at all, not
one booted with ACPI disabled), such systems were there in the field ~30
years ago and most likely they would not be able to run a contemporary
Linux kernel.

For the above reasons, drop the PNP device check from add_rtc_cmos().

Signed-off-by: Rafael J. Wysocki 
Acked-by: Dave Hansen  # x86
Link: https://patch.msgid.link/8660687.T7Z3S40VBb@rafael.j.wysocki

ACPI: x86: cmos_rtc: Create a CMOS RTC platform device

2026-02-26T17:46:04+00:00

Make the CMOS RTC ACPI scan handler create a platform device that will
be used subsequently by rtc-cmos for driver binding on x86 systems with
ACPI and update add_rtc_cmos() to skip registering a fallback platform
device for the CMOS RTC when the above one has been registered.

Signed-off-by: Rafael J. Wysocki 
Acked-by: Dave Hansen  # x86
Link: https://patch.msgid.link/1962427.tdWV9SEqCh@rafael.j.wysocki

x86/rtc: Remove unused intel-mid.h

2024-04-03T15:24:48+00:00

The rtc driver used to be disabled with a direct check for Intel MID
platforms.  But that direct check was replaced long ago (see second
link).  Remove the (unused since 2016) include.

[ dhansen: rewrite changelog to include some history ]

Signed-off-by: Andy Shevchenko 
Signed-off-by: Dave Hansen 
Link: https://lore.kernel.org/all/20240305161024.1364098-1-andriy.shevchenko%40linux.intel.com
Link: https://lore.kernel.org/all/1460592286-300-5-git-send-email-mcgrof@kernel.org

rtc: Extend timeout for waiting for UIP to clear to 1s

2023-12-17T21:33:55+00:00

Specs don't say anything about UIP being cleared within 10ms. They
only say that UIP won't occur for another 244uS. If a long NMI occurs
while UIP is still updating it might not be possible to get valid
data in 10ms.

This has been observed in the wild that around s2idle some calls can
take up to 480ms before UIP is clear.

Adjust callers from outside an interrupt context to wait for up to a
1s instead of 10ms.

Cc:   # 6.1.y
Fixes: ec5895c0f2d8 ("rtc: mc146818-lib: extract mc146818_avoid_UIP")
Reported-by: Carsten Hatger 
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217626
Tested-by: Mateusz Jończyk 
Reviewed-by: Mateusz Jończyk 
Acked-by: Mateusz Jończyk 
Signed-off-by: Mario Limonciello 
Link: https://lore.kernel.org/r/20231128053653.101798-5-mario.limonciello@amd.com
Signed-off-by: Alexandre Belloni

rtc: Add support for configuring the UIP timeout for RTC reads

2023-12-17T21:33:55+00:00

The UIP timeout is hardcoded to 10ms for all RTC reads, but in some
contexts this might not be enough time. Add a timeout parameter to
mc146818_get_time() and mc146818_get_time_callback().

If UIP timeout is configured by caller to be >=100 ms and a call
takes this long, log a warning.

Make all callers use 10ms to ensure no functional changes.

Cc:   # 6.1.y
Fixes: ec5895c0f2d8 ("rtc: mc146818-lib: extract mc146818_avoid_UIP")
Signed-off-by: Mario Limonciello 
Tested-by: Mateusz Jończyk 
Reviewed-by: Mateusz Jończyk 
Acked-by: Mateusz Jończyk 
Link: https://lore.kernel.org/r/20231128053653.101798-4-mario.limonciello@amd.com
Signed-off-by: Alexandre Belloni

x86/rtc: Simplify PNP ids check

2023-01-06T03:22:34+00:00

compare_pnp_id() already iterates over the single linked pnp_ids list
starting with the id past to it.

So there is no need for add_rtc_cmos() to call compare_pnp_id()
for each id on the list.

No change in functionality intended.

Signed-off-by: Hans de Goede 
Signed-off-by: Ingo Molnar 
Acked-by: Rafael J. Wysocki 
Cc: linux-kernel@vger.kernel.org

x86/rtc: Rename mach_set_rtc_mmss() to mach_set_cmos_time()

2022-08-14T09:24:29+00:00

Once upon a time, before this commit in 2013:

   3195ef59cb42 ("x86: Do full rtc synchronization with ntp")

... the mach_set_rtc_mmss() function set only the minutes and seconds
registers of the CMOS RTC - hence the '_mmss' postfix.

This is no longer true, so rename the function to mach_set_cmos_time().

[ mingo: Expanded changelog a bit. ]

Signed-off-by: Mateusz Jończyk 
Signed-off-by: Ingo Molnar 
Link: https://lore.kernel.org/r/20220813131034.768527-2-mat.jonczyk@o2.pl

x86/rtc: Rewrite & simplify mach_get_cmos_time() by deleting duplicated functionality

2022-08-14T09:24:08+00:00

There are functions in drivers/rtc/rtc-mc146818-lib.c that handle
reading from / writing to the CMOS RTC clock. mach_get_cmos_time() in
arch/x86/kernel/rtc.c did not use them and was mostly a duplicate of
mc146818_get_time(). Modify mach_get_cmos_time() to use
mc146818_get_time() and remove the duplicated functionality.

mach_get_cmos_time() used a different algorithm than
mc146818_get_time(), but these functions are equivalent. The major
differences are:

- mc146818_get_time() is better refined and handles various edge
  conditions,

- when the UIP ("Update in progress") bit of the RTC is set,
  mach_get_cmos_time() was busy waiting with cpu_relax() while
  mc146818_get_time() is using mdelay(1) in every loop iteration.
  (However, there is my commit merged for Linux 5.20 / 6.0 to decrease
  this period to 100us:
    commit d2a632a8a117 ("rtc: mc146818-lib: reduce RTC_UIP polling period")
  ),

- mach_get_cmos_time() assumed that the RTC year is >= 2000, which
  may not be true on some old boxes with a dead battery,

- mach_get_cmos_time() was holding the rtc_lock for a long time
  and could hang if the RTC is broken or not present.

The RTC writing counterpart, mach_set_rtc_mmss() is already using
mc146818_get_time() from drivers/rtc. This was done in
        commit 3195ef59cb42 ("x86: Do full rtc synchronization with ntp")
It appears that mach_get_cmos_time() was simply forgotten.

mach_get_cmos_time() is really used only in read_persistent_clock64(),
which is called only in a few places in kernel/time/timekeeping.c .

[ mingo: These changes are not supposed to change behavior, but they are
         not identity transformations either, as mc146818_get_time() is a
	 better but different implementation of the same logic - so
	 regressions are possible in principle. ]

Signed-off-by: Mateusz Jończyk 
Signed-off-by: Ingo Molnar 
Acked-by: Alexandre Belloni 
Link: https://lore.kernel.org/r/20220813131034.768527-1-mat.jonczyk@o2.pl

x86: Convert x86_platform_ops to timespec64

2018-05-19T12:03:14+00:00

The x86 platform operations are fairly isolated, so it's easy to change
them from using timespec to timespec64. It has been checked that all the
users and callers are safe, and there is only one critical function that is
broken beyond 2106:

  pvclock_read_wallclock() uses a 32-bit number of seconds since the epoch
  to communicate the boot time between host and guest in a virtual
  environment. This will work until 2106, but fixing this is outside the
  scope of this change, Add a comment at least.

Signed-off-by: Arnd Bergmann 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Boris Ostrovsky 
Acked-by: Radim Krčmář 
Acked-by: Jan Kiszka 
Cc: Juergen Gross 
Cc: jailhouse-dev@googlegroups.com
Cc: Borislav Petkov 
Cc: kvm@vger.kernel.org
Cc: y2038@lists.linaro.org
Cc: "Rafael J. Wysocki" 
Cc: xen-devel@lists.xenproject.org
Cc: John Stultz 
Cc: Andy Lutomirski 
Cc: "H. Peter Anvin" 
Cc: Paolo Bonzini 
Cc: Andy Shevchenko 
Cc: Joao Martins 
Link: https://lkml.kernel.org/r/20180427201435.3194219-1-arnd@arndb.de

x86/rtc: Stop using deprecated functions

2018-03-15T08:47:24+00:00

rtc_time_to_tm() and rtc_tm_to_time() are deprecated because they
rely on 32bits variables and that will make rtc break in y2038/2016.

Use the proper y2038 safe functions.

Signed-off-by: Benjamin Gaignard 
Signed-off-by: John Stultz 
Signed-off-by: Thomas Gleixner 
Cc: Prarit Bhargava 
Cc: Arnd Bergmann 
Cc: Richard Cochran 
Cc: Stephen Boyd 
Cc: Miroslav Lichvar 
Cc: Alexandre Belloni 
Link: https://lkml.kernel.org/r/1520620971-9567-5-git-send-email-john.stultz@linaro.org