On Saturday 02 February 2008, Pavel Machek wrote:
> Hi!
>
> > > --- a/drivers/rtc/rtc-cmos.c
> > > +++ b/drivers/rtc/rtc-cmos.c
> > > @@ -78,7 +78,7 @@ static inline int is_intr(u8 rtc_intr)
> > >
> > > /*----------------------------------------------------------------*/
> > >
> > > -static int cmos_read_time(struct device *dev, struct rtc_time *t)
> > > +int cmos_read_time(struct device *dev, struct rtc_time *t)
> > > {
> > >
> > > ... etc ...
> >
> > You should be using the standard RTC library calls, exported
> > from drivers/rtc/interface.c ... and making sure this mechanism
> > will work with any wakeup-capable RTC. Otherwise you'll end
> > being needlessly x86-specific, or reinventing those calls.
> >
> > Plus, the way you're doing it now is violating the locking
> > protocol used by that driver.
>
> Yep, you are right, but that is the easy issue to fix.
Which is why I was puzzled that you didn't start out doing it
the "right" way ... even just hard-wiring the dubious assumption
that "rtc0" is the right RTC to use. :)
> There's hard issue: I need
>
> struct rtc_device *rtc
>
> for the rtc that can be used for system resume,
Well, "rtc which (a) has an alarm, (b) may be used for system wakeup".
Assuming there *is* such an RTC ... fortunately, there will usually be
one on systems that are designed to go to sleep.
> and I'd like to get it
> without violating too many layers. How to do that?
>
> Ideally, I need
>
> set_alarm(int)
>
> ...that will magically pick the right rtc device to talk to, and set
> alarm on it. I don't see how to implement it with current code.
Easy enough. Given an RTC device node, you can tell whether it has
no chance at all to meet those requirements:
static int has_wakealarm(struct device *dev, void *name_ptr)
{
struct rtc_device *rtc = to_rtc_device(dev);
/* (a) has an alarm */
if (!rtc->op->set_alarm)
return 0;
/* (b) may be used for system wakeup */
if (device_may_wakeup(dev->parent))
return 0;
*(char **)name_ptr = rtc->name;
return 1;
}
Then there's a new class interface you may not have known about,
since it's been merged barely over a week now. You can use it
to find the name of the rtc to pass to rtc_open():
static char *find_wake_rtc(void)
{
char *pony = NULL;
dev = class_find_device(rtc_class, &rtc, has_wakealarm);
return pony;
}
On most PCs that will return the name "rtc0" ... and it'll do
the same on most of the other systems I have. On both of the
two-RTC systems I have that will return "rtc1". On systems
with no wakealarm-enabled RTC, that will return NULL.
Voila!
- Dave
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