On 14/08/2020 16:10:13+1000, Victor Ding wrote: > 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. > Seeing that saved_wkalrm is initialized to zero, wouldn't it be sufficient to initialize current_alarm to 0? This can be done simply at the declaration. I personally find the -1 to be confusing especially since the result ends up being architecture dependent. > > > > > 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 -- Alexandre Belloni, Bootlin Embedded Linux and Kernel engineering https://bootlin.com
