--- /dev/null
+From fe9f5f96cfe8b82d0f24cbfa93718925560f4f8d Mon Sep 17 00:00:00 2001
+From: Alexandre Mergnat <amergnat@baylibre.com>
+Date: Mon, 28 Apr 2025 12:06:48 +0200
+Subject: rtc: Fix offset calculation for .start_secs < 0
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+From: Alexandre Mergnat <amergnat@baylibre.com>
+
+commit fe9f5f96cfe8b82d0f24cbfa93718925560f4f8d upstream.
+
+The comparison
+
+ rtc->start_secs > rtc->range_max
+
+has a signed left-hand side and an unsigned right-hand side.
+So the comparison might become true for negative start_secs which is
+interpreted as a (possibly very large) positive value.
+
+As a negative value can never be bigger than an unsigned value
+the correct representation of the (mathematical) comparison
+
+ rtc->start_secs > rtc->range_max
+
+in C is:
+
+ rtc->start_secs >= 0 && rtc->start_secs > rtc->range_max
+
+Use that to fix the offset calculation currently used in the
+rtc-mt6397 driver.
+
+Fixes: 989515647e783 ("rtc: Add one offset seconds to expand RTC range")
+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-v4-2-2b2f7e3f9349@baylibre.com
+Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
+Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ drivers/rtc/class.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+--- a/drivers/rtc/class.c
++++ b/drivers/rtc/class.c
+@@ -323,7 +323,7 @@ static void rtc_device_get_offset(struct
+ *
+ * Otherwise the offset seconds should be 0.
+ */
+- if (rtc->start_secs > rtc->range_max ||
++ if ((rtc->start_secs >= 0 && rtc->start_secs > rtc->range_max) ||
+ rtc->start_secs + range_secs - 1 < rtc->range_min)
+ rtc->offset_secs = rtc->start_secs - rtc->range_min;
+ else if (rtc->start_secs > rtc->range_min)
--- /dev/null
+From 7df4cfef8b351fec3156160bedfc7d6d29de4cce Mon Sep 17 00:00:00 2001
+From: Alexandre Mergnat <amergnat@baylibre.com>
+Date: Mon, 28 Apr 2025 12:06:47 +0200
+Subject: rtc: Make rtc_time64_to_tm() support dates before 1970
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+From: Alexandre Mergnat <amergnat@baylibre.com>
+
+commit 7df4cfef8b351fec3156160bedfc7d6d29de4cce upstream.
+
+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>
+Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ drivers/rtc/lib.c | 24 +++++++++++++++++++-----
+ 1 file changed, 19 insertions(+), 5 deletions(-)
+
+--- a/drivers/rtc/lib.c
++++ b/drivers/rtc/lib.c
+@@ -46,24 +46,38 @@ EXPORT_SYMBOL(rtc_year_days);
+ * rtc_time64_to_tm - converts time64_t to rtc_time.
+ *
+ * @time: The number of seconds since 01-01-1970 00:00:00.
+- * (Must be positive.)
++ * Works for values since at least 1900
+ * @tm: Pointer to the struct rtc_time.
+ */
+ void rtc_time64_to_tm(time64_t time, struct rtc_time *tm)
+ {
+- unsigned int secs;
+- int days;
++ int days, secs;
+
+ u64 u64tmp;
+ u32 u32tmp, udays, century, day_of_century, year_of_century, year,
+ day_of_year, month, day;
+ bool is_Jan_or_Feb, is_leap_year;
+
+- /* time must be positive */
++ /*
++ * Get days and seconds while preserving the sign to
++ * handle negative time values (dates before 1970-01-01)
++ */
+ days = div_s64_rem(time, 86400, &secs);
+
++ /*
++ * We need 0 <= secs < 86400 which isn't given for negative
++ * values of time. Fixup accordingly.
++ */
++ if (secs < 0) {
++ days -= 1;
++ secs += 86400;
++ }
++
+ /* day of the week, 1970-01-01 was a Thursday */
+ tm->tm_wday = (days + 4) % 7;
++ /* Ensure tm_wday is always positive */
++ if (tm->tm_wday < 0)
++ tm->tm_wday += 7;
+
+ /*
+ * The following algorithm is, basically, Proposition 6.3 of Neri
+@@ -93,7 +107,7 @@ void rtc_time64_to_tm(time64_t time, str
+ * thus, is slightly different from [1].
+ */
+
+- udays = ((u32) days) + 719468;
++ udays = days + 719468;
+
+ u32tmp = 4 * udays + 3;
+ century = u32tmp / 146097;
projects / thirdparty / kernel / stable-queue.git / commitdiff
