[PATCH 5.10 038/106] rtc: cmos: avoid UIP when writing alarm time

Greg Kroah-Hartman
2022-12-12T13:14:17Z

From: Mateusz Jończyk <mat.jonczyk@o2.pl>

[ Upstream commit cd17420ebea580c22dd3a93f7237de3d2cfafc37 ]

Some Intel chipsets disconnect the time and date RTC registers when the
clock update is in progress: during this time reads may return bogus
values and writes fail silently. This includes the RTC alarm registers.
[1]

cmos_set_alarm() did not take account for that, fix it.

[1] 7th Generation Intel ® Processor Family I/O for U/Y Platforms [...]
Datasheet, Volume 1 of 2 (Intel's Document Number: 334658-006)
Page 208
https://www.intel.com/content/dam/www/public/us/en/documents/datasheets/7th-and-8th-gen-core-family-mobile-u-y-processor-lines-i-o-datasheet-vol-1.pdf
"If a RAM read from the ten time and date bytes is attempted
during an update cycle, the value read do not necessarily
represent the true contents of those locations. Any RAM writes
under the same conditions are ignored."

Signed-off-by: Mateusz Jończyk <mat.jonczyk@o2.pl>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20211210200131.153887-10-mat.jonczyk@o2.pl
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/rtc/rtc-cmos.c | 107 +++++++++++++++++++++++++----------------
1 file changed, 66 insertions(+), 41 deletions(-)

diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
index 93ffb9eaf63a..601e3967e1f0 100644
--- a/drivers/rtc/rtc-cmos.c
+++ b/drivers/rtc/rtc-cmos.c
@@ -444,10 +444,57 @@ static int cmos_validate_alarm(struct device *dev, struct rtc_wkalrm *t)
return 0;
}

+struct cmos_set_alarm_callback_param {
+ struct cmos_rtc *cmos;
+ unsigned char mon, mday, hrs, min, sec;
+ struct rtc_wkalrm *t;
+};
+
+/* Note: this function may be executed by mc146818_avoid_UIP() more then
+ * once
+ */
+static void cmos_set_alarm_callback(unsigned char __always_unused seconds,
+ void *param_in)
+{
+ struct cmos_set_alarm_callback_param *p =
+ (struct cmos_set_alarm_callback_param *)param_in;
+
+ /* next rtc irq must not be from previous alarm setting */
+ cmos_irq_disable(p->cmos, RTC_AIE);
+
+ /* update alarm */
+ CMOS_WRITE(p->hrs, RTC_HOURS_ALARM);
+ CMOS_WRITE(p->min, RTC_MINUTES_ALARM);
+ CMOS_WRITE(p->sec, RTC_SECONDS_ALARM);
+
+ /* the system may support an "enhanced" alarm */
+ if (p->cmos->day_alrm) {
+ CMOS_WRITE(p->mday, p->cmos->day_alrm);
+ if (p->cmos->mon_alrm)
+ CMOS_WRITE(p->mon, p->cmos->mon_alrm);
+ }
+
+ if (use_hpet_alarm()) {
+ /*
+ * FIXME the HPET alarm glue currently ignores day_alrm
+ * and mon_alrm ...
+ */
+ hpet_set_alarm_time(p->t->time.tm_hour, p->t->time.tm_min,
+ p->t->time.tm_sec);
+ }
+
+ if (p->t->enabled)
+ cmos_irq_enable(p->cmos, RTC_AIE);
+}
+
static int cmos_set_alarm(struct device *dev, struct rtc_wkalrm *t)
{
struct cmos_rtc *cmos = dev_get_drvdata(dev);
- unsigned char mon, mday, hrs, min, sec, rtc_control;
+ struct cmos_set_alarm_callback_param p = {
+ .cmos = cmos,
+ .t = t
+ };
+ unsigned char rtc_control;
int ret;

/* This not only a rtc_op, but also called directly */
@@ -458,11 +505,11 @@ static int cmos_set_alarm(struct device *dev, struct rtc_wkalrm *t)
if (ret < 0)
return ret;

- mon = t->time.tm_mon + 1;
- mday = t->time.tm_mday;
- hrs = t->time.tm_hour;
- min = t->time.tm_min;
- sec = t->time.tm_sec;
+ p.mon = t->time.tm_mon + 1;
+ p.mday = t->time.tm_mday;
+ p.hrs = t->time.tm_hour;
+ p.min = t->time.tm_min;
+ p.sec = t->time.tm_sec;

spin_lock_irq(&rtc_lock);
rtc_control = CMOS_READ(RTC_CONTROL);
@@ -470,43 +517,21 @@ static int cmos_set_alarm(struct device *dev, struct rtc_wkalrm *t)

if (!(rtc_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
/* Writing 0xff means "don't care" or "match all". */
- mon = (mon <= 12) ? bin2bcd(mon) : 0xff;
- mday = (mday >= 1 && mday <= 31) ? bin2bcd(mday) : 0xff;
- hrs = (hrs < 24) ? bin2bcd(hrs) : 0xff;
- min = (min < 60) ? bin2bcd(min) : 0xff;
- sec = (sec < 60) ? bin2bcd(sec) : 0xff;
+ p.mon = (p.mon <= 12) ? bin2bcd(p.mon) : 0xff;
+ p.mday = (p.mday >= 1 && p.mday <= 31) ? bin2bcd(p.mday) : 0xff;
+ p.hrs = (p.hrs < 24) ? bin2bcd(p.hrs) : 0xff;
+ p.min = (p.min < 60) ? bin2bcd(p.min) : 0xff;
+ p.sec = (p.sec < 60) ? bin2bcd(p.sec) : 0xff;
}

- spin_lock_irq(&rtc_lock);
-
- /* next rtc irq must not be from previous alarm setting */
- cmos_irq_disable(cmos, RTC_AIE);
-
- /* update alarm */
- CMOS_WRITE(hrs, RTC_HOURS_ALARM);
- CMOS_WRITE(min, RTC_MINUTES_ALARM);
- CMOS_WRITE(sec, RTC_SECONDS_ALARM);
-
- /* the system may support an "enhanced" alarm */
- if (cmos->day_alrm) {
- CMOS_WRITE(mday, cmos->day_alrm);
- if (cmos->mon_alrm)
- CMOS_WRITE(mon, cmos->mon_alrm);
- }
-
- if (use_hpet_alarm()) {
- /*
- * FIXME the HPET alarm glue currently ignores day_alrm
- * and mon_alrm ...
- */
- hpet_set_alarm_time(t->time.tm_hour, t->time.tm_min,
- t->time.tm_sec);
- }
-
- if (t->enabled)
- cmos_irq_enable(cmos, RTC_AIE);
-
- spin_unlock_irq(&rtc_lock);
+ /*
+ * Some Intel chipsets disconnect the alarm registers when the clock
+ * update is in progress - during this time writes fail silently.
+ *
+ * Use mc146818_avoid_UIP() to avoid this.
+ */
+ if (!mc146818_avoid_UIP(cmos_set_alarm_callback, &p))
+ return -EIO;

cmos->alarm_expires = rtc_tm_to_time64(&t->time);

--
2.35.1