Recently (in commit 7df4cfef8b ("rtc: Make rtc_time64_to_tm() support
dates before 1970")) the function rtc_time64_to_tm() was repaired for
times before 1970. This introduced two if blocks. Cassio Neri pointed
out that to be not neccessary and suggested an adaption that allows to
drop the two branch points again.
This is implemented here.
Also adapt the reference to the theoretical paper to link to the final
published article instead of the preprint on Cassio's request.
Suggested-by: Cassio Neri <cassio.neri@gmail.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://lore.kernel.org/r/20250613142405.253420-2-u.kleine-koenig@baylibre.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Conversion of dates before 1970 is still relevant today because these
dates are reused on some hardwares to store dates bigger than the
maximal date that is representable in the device's native format.
This prominently and very soon affects the hardware covered by the
rtc-mt6397 driver that can only natively store dates in the interval
1900-01-01 up to 2027-12-31. So to store the date 2028-01-01 00:00:00
to such a device, rtc_time64_to_tm() must do the right thing for
time=-2208988800.
Signed-off-by: Alexandre Mergnat <amergnat@baylibre.com>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://lore.kernel.org/r/20250428-enable-rtc-v4-1-2b2f7e3f9349@baylibre.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
The current implementation of rtc_time64_to_tm() contains unnecessary
loops, branches and look-up tables. The new one uses an arithmetic-based
algorithm appeared in [1] and is approximately 4.3 times faster (YMMV).
The drawback is that the new code isn't intuitive and contains many 'magic
numbers' (not unusual for this type of algorithm). However, [1] justifies
all those numbers and, given this function's history, the code is unlikely
to need much maintenance, if any at all.
Add a KUnit test case that checks every day in a 160,000 years interval
starting on 1970-01-01 against the expected result. Add a new config
RTC_LIB_KUNIT_TEST symbol to give the option to run this test suite.
[1] Neri, Schneider, "Euclidean Affine Functions and Applications to
Calendar Algorithms". https://arxiv.org/abs/2102.06959
Signed-off-by: Cassio Neri <cassio.neri@gmail.com>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20210624201343.85441-1-cassio.neri@gmail.com
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>
Users may call 'ioctl' and pass a very big value on 'tm->tm_year'.
It can be overflowed in 'int' after add 1900.
In function 'rtc_month_days' and 'mktime64', also treated it as an
'unsigned' parameter.
UBSAN: Undefined behaviour in drivers/rtc/rtc-lib.c:103:59
signed integer overflow:
2147483647 + 1900 cannot be represented in type 'int'
UBSAN: Undefined behaviour in drivers/rtc/rtc-lib.c:119:30
signed integer overflow:
2147483647 + 1900 cannot be represented in type 'int'
So, covert it to 'unsigned' explicitly.
Signed-off-by: ZhangXiaoxu <zhangxiaoxu5@huawei.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
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>
