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From: Bijan Mottahedeh <bijan.mottahedeh@oracle.com>
Message-ID: <7cfea6b6-b0eb-f276-edc7-da2e7f77ded0@oracle.com>
Date: Fri, 9 Nov 2018 19:12:08 -0800
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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: Richard Henderson <richard.henderson@linaro.org>, qemu-devel@nongnu.org
Cc: kvmarm@lists.cs.columbia.edu, Karl Heubaum <karl.heubaum@oracle.com>

On 11/8/2018 6:21 AM, Richard Henderson wrote:
> 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~
Is it ok to ifdef the asm statement with CONFIG_KVM, or what would be 
the correct way to account for TCG vs. KVM?

Thanks.

--bijan