Hi Alexandre, On Thu, Aug 13, 2020 at 5:33 PM Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx> wrote: > > Hi, > > On 13/08/2020 15:41:34+1000, Victor Ding wrote: > > cmos_read_alarm() may leave certain fields of a struct rtc_time > > untouched; therefore, these fields contain garbage if not properly > > initialized, leading to inconsistent values when converting into > > time64_t. > > This patch to set all fields of a struct rtc_time to -1 before calling > > cmos_read_alarm(). > > > > I don't think this actually helps with the conversion as mktime64 > is taking unsigned int so I would think you need the whole logic that is > in __rtc_read_alarm It's true that this change does not produce a correct time64_t; however, it isn't the intention either. The proposed change only produces a consistent value: calling obtaining identical struct rtc_time if the CMOS wakealarm is unchanged. In the case of suspend/resume, a correct value time64_t is not necessary; a consistent value is sufficient to correctly perform an equality test for `t_current_expires` and `t_saved_expires`. Logic to deduce a correct time64_t is expensive and hence I would like to avoid __rtc_read_alarm's logic here. Prior to this patch, the struct rtc_time is uninitialized. After calling cmos_read_alarm(), the tm_year field is always left untouched and hence contains only garbage. On platforms without enhanced RTC timers, the tm_mon and tm_mday fields are left with garbage as well. Therefore, `t_current_expires` and `t_saved_expires` from garbage data, which leads to incorrect equality test results. > > > Signed-off-by: Victor Ding <victording@xxxxxxxxxx> > > --- > > > > drivers/rtc/rtc-cmos.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c > > index bcc96ab7793f..c99af567780d 100644 > > --- a/drivers/rtc/rtc-cmos.c > > +++ b/drivers/rtc/rtc-cmos.c > > @@ -1006,6 +1006,7 @@ static int cmos_suspend(struct device *dev) > > enable_irq_wake(cmos->irq); > > } > > > > + memset(&cmos->saved_wkalrm.time, -1, sizeof(struct rtc_time)); > > cmos_read_alarm(dev, &cmos->saved_wkalrm); > > > > dev_dbg(dev, "suspend%s, ctrl %02x\n", > > @@ -1054,6 +1055,7 @@ static void cmos_check_wkalrm(struct device *dev) > > return; > > } > > > > + memset(¤t_alarm.time, -1, sizeof(struct rtc_time)); > > cmos_read_alarm(dev, ¤t_alarm); > > t_current_expires = rtc_tm_to_time64(¤t_alarm.time); > > t_saved_expires = rtc_tm_to_time64(&cmos->saved_wkalrm.time); > > -- > > 2.28.0.236.gb10cc79966-goog > > > > -- > Alexandre Belloni, Bootlin > Embedded Linux and Kernel engineering > https://bootlin.com Best regards, Victor Ding