From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ulrich Obergfell <uobergfe@redhat.com>
Subject: Re: [PATCH v3 5/5] hpet 'driftfix': add code in
 hpet_timer() to compensate delayed callbacks and coalesced interrupts
Date: Thu, 5 May 2011 04:07:19 -0400 (EDT)
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Cc: aliguori@us.ibm.com, kvm@vger.kernel.org,
	jan kiszka <jan.kiszka@siemens.com>, qemu-devel@nongnu.org,
	gcosta@redhat.com, avi@redhat.com
To: Marcelo Tosatti <mtosatti@redhat.com>
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Hi Marcelo,
 
> Other than that, shouldnt reset accounting variables to init state on
> write to GLOBAL_ENABLE_CFG / writes to main counter?

I'd suggest to initialize/reset the driftfix-related fields in the
'HPETTimer' structure (including the backlog of unaccounted ticks)
in the following situations.


- When the guest o/s sets the 'CFG_ENABLE' bit (overall enable) in
  the General Configuration Register.

  This is the place in hpet_ram_writel():

        case HPET_CFG:
            ...
            if (activating_bit(old_val, new_val, HPET_CFG_ENABLE)) {
                ...
                for (i = 0; i < s->num_timers; i++) {
                    if ((&s->timer[i])->cmp != ~0ULL) {
                        // initialize / reset fields here
                        hpet_set_timer(&s->timer[i]);


- When the guest o/s sets the 'TN_ENABLE' bit (timer N interrupt
  enable) in the Timer N Configuration and Capabilities Register.

  This is the place in hpet_ram_writel():

        case HPET_TN_CFG:
            ...
            if (activating_bit(old_val, new_val, HPET_TN_ENABLE)) {
                // initialize / reset fields here
                hpet_set_timer(timer);


This should cover cases such as ...

- first time initialization of HPET & timers during guest o/s boot.
  (includes kexec and reboot)

- if a guest o/s stops and restarts the timer.
  (for example, to change the comparator register value or
   to switch a timer between periodic mode and non-periodic mode)


Regards,

Uli