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Date: Mon, 16 Dec 2013 20:46:58 -0800
From: Christoffer Dall <christoffer.dall@linaro.org>
Message-ID: <20131217044658.GI5711@cbox>
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Subject: Re: [Qemu-devel] [PATCH 3/7] target-arm: Add minimal KVM AArch64
	support
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: Patch Tracking <patches@linaro.org>, QEMU Developers <qemu-devel@nongnu.org>, "kvmarm@lists.cs.columbia.edu" <kvmarm@lists.cs.columbia.edu>

On Tue, Dec 17, 2013 at 12:21:27AM +0000, Peter Maydell wrote:
> On 16 December 2013 23:39, Christoffer Dall <christoffer.dall@linaro.org> wrote:
> > On Thu, Nov 28, 2013 at 01:33:18PM +0000, Peter Maydell wrote:
> >> +    ahcc->target = init.target;
> >> +    ahcc->dtb_compatible = "arm,arm-v7";
> >
> > arm,arm-v8 ?
> 
> Oops, yes, cut-n-pasto.
> 
> 
> >
> >> +
> >> +    kvm_arm_destroy_scratch_host_vcpu(fdarray);
> >> +
> >> +   /* We can assume any KVM supporting CPU is at least a v8
> >> +     * with VFPv4+Neon; this in turn implies most of the other
> >> +     * feature bits.
> >
> > not sure I understand the bit about implying other feature bits, the
> > only other thing we're setting here is AARCH64 and the features bits are
> > enum values?
> 
> target-arm/cpu.c:cpu_realize_fn() has a large set of if statements
> like
> 
>     if (arm_feature(env, ARM_FEATURE_V8)) {
>         set_feature(env, ARM_FEATURE_V7);
>         set_feature(env, ARM_FEATURE_ARM_DIV);
>         set_feature(env, ARM_FEATURE_LPAE);
>     }
> 
> because architecturally some features or arch versions imply
> that you have others (eg above v8 means we always know
> we have LPAE and division)...
> 
> >> +     */
> >> +    set_feature(&features, ARM_FEATURE_V8);
> >> +    set_feature(&features, ARM_FEATURE_VFP4);
> >> +    set_feature(&features, ARM_FEATURE_NEON);
> >> +    set_feature(&features, ARM_FEATURE_AARCH64);
> 
> ...and because presence of the 'v8', 'vfp4', 'neon' features implies
> (as enforced via those if statements) presence of just about every
> other feature it means we don't need to have specific
> tests for "do the CPU's feature registers say we support
> division?" like the v7 KVM code does, because we know
> that it's all implied automatically.
> 
Got it, I was looking for something like that, but somehow missed the
realize function.  Thanks!