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Date:   Mon, 28 Apr 2014 17:42:49 +0200
From:   Paolo Bonzini <pbonzini@redhat.com>
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To:     James Hogan <james.hogan@imgtec.com>
CC:     Gleb Natapov <gleb@kernel.org>, kvm@vger.kernel.org,
        Ralf Baechle <ralf@linux-mips.org>,
        Linux MIPS Mailing List <linux-mips@linux-mips.org>,
        David Daney <david.daney@cavium.com>,
        Sanjay Lal <sanjayl@kymasys.com>
Subject: Re: [PATCH 14/21] MIPS: KVM: Add nanosecond count bias KVM register
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Il 28/04/2014 17:17, James Hogan ha scritto:
>> > If it is possible and not too hairy to use a raw value in userspace
>> > (together with KVM_REG_MIPS_COUNT_HZ), please do it---my suggestions were
>> > just that, a suggestion.  Otherwise, the patch looks good.
> Do you mean expose the raw internal offset to userland instead of the
> nanosecond one? Yeh it should be possible & slightly simpler for both
> kernel and Qemu actually.

Yes, when I reviewed the QEMU patches I missed this consequence of 
exposing the HZ.

> Qemu could then store that value (or the Count register) straight into
> env->CP0_Count (depending on Cause.DC), then hw/mips/cputimer.c would
> pretty much continue to work accurately. cputimer.c is only really
> made use of by tcg at the moment though (reading/writing
> count/compare/cause.DC), but it still makes sense to be consistent.

Yup.  cputimer.c would just use a HZ value stored in CPUMIPSState 
(TIMER_FREQ for TCG) instead of hardcoding TIMER_FREQ I guess.

Paolo