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References: <1541616504-68526-1-git-send-email-bijan.mottahedeh@oracle.com>
	<1541616504-68526-2-git-send-email-bijan.mottahedeh@oracle.com>
From: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <47f78310-56e7-ba5e-0fb1-99830750e49b@linaro.org>
Date: Thu, 8 Nov 2018 15:21:47 +0100
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Subject: Re: [Qemu-devel] [RFC QEMU 1/2] arm/virt: Initialize generic timer
 scale factor dynamically
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To: Bijan Mottahedeh <bijan.mottahedeh@oracle.com>, qemu-devel@nongnu.org
Cc: kvmarm@lists.cs.columbia.edu

On 11/7/18 7:48 PM, Bijan Mottahedeh wrote:
>  
> +static void set_system_clock_scale(void)
> +{
> +    unsigned long cntfrq_el0;
> +
> +    asm volatile("mrs %0, cntfrq_el0" : "=r"(cntfrq_el0));
> +
> +    if (cntfrq_el0 == 0) {
> +        cntfrq_el0 = GTIMER_SCALE_DEF;
> +    }
> +
> +    system_clock_scale = NANOSECONDS_PER_SECOND / (int)cntfrq_el0;
> +}

This only works for kvm.

For TCG you need to use the default always.  In particular, it won't even
compile for an x86 host.


r~

From mboxrd@z Thu Jan  1 00:00:00 1970
From: Richard Henderson <richard.henderson@linaro.org>
Subject: Re: [RFC QEMU 1/2] arm/virt: Initialize generic timer
 scale factor dynamically
Date: Thu, 8 Nov 2018 15:21:47 +0100
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	<1541616504-68526-2-git-send-email-bijan.mottahedeh@oracle.com>
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To: Bijan Mottahedeh <bijan.mottahedeh@oracle.com>, qemu-devel@nongnu.org
Cc: kvmarm@lists.cs.columbia.edu
List-Id: kvmarm@lists.cs.columbia.edu

On 11/7/18 7:48 PM, Bijan Mottahedeh wrote:
>  
> +static void set_system_clock_scale(void)
> +{
> +    unsigned long cntfrq_el0;
> +
> +    asm volatile("mrs %0, cntfrq_el0" : "=r"(cntfrq_el0));
> +
> +    if (cntfrq_el0 == 0) {
> +        cntfrq_el0 = GTIMER_SCALE_DEF;
> +    }
> +
> +    system_clock_scale = NANOSECONDS_PER_SECOND / (int)cntfrq_el0;
> +}

This only works for kvm.

For TCG you need to use the default always.  In particular, it won't even
compile for an x86 host.


r~