On Wed, 2008-05-28 at 09:27 +0300, Avi Kivity wrote:
> This is
> > commit ce35c9534137b71327466fa9abc243cbe2d7e8dc
> > Author: Avi Kivity <[EMAIL PROTECTED]>
> > Date: Wed Jan 2 12:52:28 2008 +0200
> >
> > kvm: qemu: fix power management timer overflow handling
> >
> > The PMSTS overflow bit needs to be set each time bit 23 of the pm
> > timer
> > is toggled. This means we need to adjust the overflow time every time
> > we have an overflow.
> >
> > Taken from qemu patch by TeLeMan in
> >
> > http://www.mail-archive.com/[EMAIL PROTECTED]/msg14680.html
>
> And, like the explanation says, we have to advance the overflow time in
> order to get an interrupt. Is there something horribly broken?
Yeah, it kinda seems like there is. With this change, the timer expires
and we go through this path:
pm_tmr_timer()
-> pm_update_sci()
-> get_pmsts()
-> qemu_set_irq() [but not for a TMFOF_EN]
-> qemu_mod_timer()
bump tmr_overlfow_time
We bumped tmr_overflow_time in pm_update_sci after setting the timer to
expire on the old value. Unless something goes horribly wrong with
timers, we'll always get the timer event before overflow time and
get_pmsts never adds in the TMROF_EN bit to the status flag. We
therefore never toggle the SCI interrupt because of a timer overflow,
and we never report a timer overflow status to the guest.
The author of this patch is correct that the timer in the original code
only goes off a couple times before we del_timer(). However, I think
the way it's supposed to work is that we set the timer overflow status,
toggle the SCI, then wait for the OSPM to come in through
pm_ioport_writew() to clear the timer overflow status, at which point we
call pm_update_sci() mod_timer and start it all over again. At least
that's the way I see it working after removing this change.
It doesn't make much sense to bump tmr_overflow_time so that we never
hit it, unless I'm completely misunderstanding the code. Thanks,
Alex
--
Alex Williamson HP Open Source & Linux Org.
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