Differential D59749

vmm: Normalize a zero PIT count before starting channel 0
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Authored by hayzam_gmail.com on Thu, Sep 17, 12:08 AM.

Details

Reviewers

markj

Group Reviewers

bhyve

Commits

rG3330226fd33a: vmm: Normalize a zero PIT count before starting channel 0

Summary

pit_timer_start_cntr0() does not schedule a callout when the initial
count is zero. The counter write handler normalizes a programmed zero
count only after calling it, leaving an initially unarmed channel 0
without a scheduled timer event.

Move the existing normalization before the timer-start call. Retain the
historical 0xffff representation of a zero count.

Diff Detail

Repository

rG FreeBSD src repository

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Lint Skipped

Unit

Tests Skipped

Build Status

Buildable 77006
Build 73889: arc lint + arc unit

Event Timeline

hayzam_gmail.com created this revision.Thu, Sep 17, 12:08 AM

Herald added a reviewer: bhyve. · View Herald TranscriptThu, Sep 17, 12:08 AM

Herald added subscribers: bcran, rgrimes, imp. · View Herald Transcript

hayzam_gmail.com requested review of this revision.Thu, Sep 17, 12:08 AM

Harbormaster completed remote builds in B77006: Diff 186927.Thu, Sep 17, 12:08 AM

How did you notice the problem?

This revision is now accepted and ready to land.Thu, Sep 17, 1:48 PM

In D59749#1371481, @markj wrote:

How did you notice the problem?

The symptom was a legacy guest hanging at the BIOS screen with its tick frozen while I was bringing up CSMWrap (https://github.com/CSMWrap/CSMWrap) on bhyve. I traced that back to SeaBIOS programming the PIT with a zero count for the normal ~18 Hz tick, which led me to this code.

Closed by commit rG3330226fd33a: vmm: Normalize a zero PIT count before starting channel 0 (authored by hayzam_gmail.com, committed by markj). · Explain WhyMon, Sep 21, 4:41 PM

This revision was automatically updated to reflect the committed changes.

markj added a commit: rG3330226fd33a: vmm: Normalize a zero PIT count before starting channel 0.