x86, hpet: Fix bug in RTC emulation
We think there exists a bug in the HPET code that emulates the RTC. In the normal case, when the RTC frequency is set, the rtc driver tells the hpet code about it here: int hpet_set_periodic_freq(unsigned long freq) { uint64_t clc; if (!is_hpet_enabled()) return 0; if (freq <= DEFAULT_RTC_INT_FREQ) hpet_pie_limit = DEFAULT_RTC_INT_FREQ / freq; else { clc = (uint64_t) hpet_clockevent.mult * NSEC_PER_SEC; do_div(clc, freq); clc >>= hpet_clockevent.shift; hpet_pie_delta = (unsigned long) clc; } return 1; } If freq is set to 64Hz (DEFAULT_RTC_INT_FREQ) or lower, then hpet_pie_limit (a static) is set to non-zero. Then, on every one-shot HPET interrupt, hpet_rtc_timer_reinit is called to compute the next timeout. Well, that function has this logic: if (!(hpet_rtc_flags & RTC_PIE) || hpet_pie_limit) delta = hpet_default_delta; else delta = hpet_pie_delta; Since hpet_pie_limit is not 0, hpet_default_delta is used. That corresponds to 64Hz. Now, if you set a different rtc frequency, you'll take the else path through hpet_set_periodic_freq, but unfortunately no one resets hpet_pie_limit back to 0. Boom....now you are stuck with 64Hz RTC interrupts forever. The patch below just resets the hpet_pie_limit value when requested freq is greater than DEFAULT_RTC_INT_FREQ, which we think fixes this problem. Signed-off-by: NAlok N Kataria <akataria@vmware.com> LKML-Reference: <201003112200.o2BM0Hre012875@imap1.linux-foundation.org> Signed-off-by: NDaniel Hecht <dhecht@vmware.com> Cc: Venkatesh Pallipadi <venkatesh.pallipadi@gmail.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by: NAndrew Morton <akpm@linux-foundation.org> Signed-off-by: NH. Peter Anvin <hpa@zytor.com>
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