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authorAlok Kataria <akataria@vmware.com>2010-03-11 17:00:16 -0500
committerH. Peter Anvin <hpa@zytor.com>2010-04-01 18:21:48 -0400
commitb4a5e8a1deca7e61ebaffb37344766b0f0e9f327 (patch)
tree9b396c3ddca5278d553448043c276fad528fcd93 /arch/x86/kernel/hpet.c
parent8da854cb02156c90028233ae1e85ce46a1d3f82c (diff)
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: Alok N Kataria <akataria@vmware.com> LKML-Reference: <201003112200.o2BM0Hre012875@imap1.linux-foundation.org> Signed-off-by: Daniel 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: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Diffstat (limited to 'arch/x86/kernel/hpet.c')
-rw-r--r--arch/x86/kernel/hpet.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
index 3d422da92100..2bda5f0052f7 100644
--- a/arch/x86/kernel/hpet.c
+++ b/arch/x86/kernel/hpet.c
@@ -1149,6 +1149,7 @@ int hpet_set_periodic_freq(unsigned long freq)
1149 do_div(clc, freq); 1149 do_div(clc, freq);
1150 clc >>= hpet_clockevent.shift; 1150 clc >>= hpet_clockevent.shift;
1151 hpet_pie_delta = clc; 1151 hpet_pie_delta = clc;
1152 hpet_pie_limit = 0;
1152 } 1153 }
1153 return 1; 1154 return 1;
1154} 1155}