On Sat, Oct 11, 2014 at 07:47:58PM -0500, Felipe Balbi wrote: > On Sat, Oct 11, 2014 at 12:12:01PM +0200, Johan Hovold wrote: > > On Fri, Oct 10, 2014 at 01:02:31PM -0500, Felipe Balbi wrote: > > > Hi, > > > > > > On Thu, Oct 09, 2014 at 09:06:30PM +0200, Johan Hovold wrote: > > > > Make sure to restore local irq state when reading the timer/calendar > > > > (TC) registers, so that omap_rtc_read_time() can be called with > > > > interrupts disabled. > > > > > > > > Signed-off-by: Johan Hovold <jo...@kernel.org> > > > > --- > > > > drivers/rtc/rtc-omap.c | 6 ++++-- > > > > 1 file changed, 4 insertions(+), 2 deletions(-) > > > > > > > > diff --git a/drivers/rtc/rtc-omap.c b/drivers/rtc/rtc-omap.c > > > > index 0ef016553a97..62e2e9a9887a 100644 > > > > --- a/drivers/rtc/rtc-omap.c > > > > +++ b/drivers/rtc/rtc-omap.c > > > > @@ -239,8 +239,10 @@ static void bcd2tm(struct rtc_time *tm) > > > > > > > > static int omap_rtc_read_time(struct device *dev, struct rtc_time *tm) > > > > { > > > > + unsigned long flags; > > > > + > > > > /* we don't report wday/yday/isdst ... */ > > > > - local_irq_disable(); > > > > + local_irq_save(flags); > > > > > > you should really convert these to a real spin_lock_irq*(), that's > > > because local_irq* do not get re-written with RT patchset, so this > > > pretty much "breaks" RT. > > > > The driver uses local_irq* throughout to guarantee registers are not > > read or written during an update event. > > > > In fact, at least on AM33xx, this is not even necessary when reading (as > > opposed to writing) the TC registers, but I did not dare change that > > without knowing how the legacy platforms work in this respect. > > > > Do you suggest doing this conversion as part of, or on top of, this > > series? > > probably on top of is. Safer that way.
I didn't include this conversion in v2 as you may have noticed. In fact, I'm not even sure it should be done. Using local_irq* "breaks" RT, but if we change it to spin_lock_irq* and RT preempts us, we may miss the 15us access window which would break the driver: "If the ARM accesses the TC registers outside of the access period, then the access is not guaranteed." On am33xx this only affects updating the TC (timer/calendar) or alarm registers, but the driver currently disables interrupts also on reading the time (possibly because the early IP revisions did not have the shadow read registers). Johan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/