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When interrupts are delayed due to interrupt masking or due to other interrupts being serviced the HPET periodic-emuation would fail. This happened because given an interval t and a time for the current interrupt m we would compute the next time as t + m. This works until we are delayed for > t, in which case we would be writing a new value which is in fact in the past. This can be solved by computing the next time instead as (k * t) + m where k is large enough to be in the future. The exact computation of k is described in a comment to the code. More detail: Assuming an interval of 5 between each expected interrupt we have a normal case of t0: interrupt, read t0 from comparator, set next interrupt t0 + 5 t5: interrupt, read t5 from comparator, set next interrupt t5 + 5 t10: interrupt, read t10 from comparator, set next interrupt t10 + 5 ... So, what happens when the interrupt is serviced too late? t0: interrupt, read t0 from comparator, set next interrupt t0 + 5 t11: delayed interrupt serviced, read t5 from comparator, set next interrupt t5 + 5, which is in the past! ... counter loops ... t10: Much much later, get the next interrupt. This can happen either because we have interrupts masked for too long (some stupid driver goes on a printk rampage) or just because we are pushing the limits of the interval (too small a period), or both most probably. My solution is to read the main counter as well and set the next interrupt to occur at the right interval, for example: t0: interrupt, read t0 from comparator, set next interrupt t0 + 5 t11: delayed interrupt serviced, read t5 from comparator, set next interrupt t15 as t10 has been missed. t15: back on track. Signed-off-by: Nils Carlson <nils.carlson@ericsson.com> Cc: John Stultz <john.stultz@linaro.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Clemens Ladisch <clemens@ladisch.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
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.. | ||
agp | ||
hw_random | ||
ipmi | ||
mwave | ||
pcmcia | ||
tpm | ||
xilinx_hwicap | ||
apm-emulation.c | ||
applicom.c | ||
applicom.h | ||
bfin-otp.c | ||
briq_panel.c | ||
bsr.c | ||
ds1302.c | ||
ds1620.c | ||
dsp56k.c | ||
dtlk.c | ||
efirtc.c | ||
generic_nvram.c | ||
genrtc.c | ||
hangcheck-timer.c | ||
hpet.c | ||
i8k.c | ||
Kconfig | ||
lp.c | ||
Makefile | ||
mbcs.c | ||
mbcs.h | ||
mem.c | ||
misc.c | ||
mmtimer.c | ||
msm_smd_pkt.c | ||
mspec.c | ||
nsc_gpio.c | ||
nvram.c | ||
nwbutton.c | ||
nwbutton.h | ||
nwflash.c | ||
pc8736x_gpio.c | ||
ppdev.c | ||
ps3flash.c | ||
ramoops.c | ||
random.c | ||
raw.c | ||
rtc.c | ||
scc.h | ||
scx200_gpio.c | ||
snsc_event.c | ||
snsc.c | ||
snsc.h | ||
sonypi.c | ||
tb0219.c | ||
tlclk.c | ||
toshiba.c | ||
ttyprintk.c | ||
uv_mmtimer.c | ||
viotape.c | ||
virtio_console.c |