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From: Rob Herring <rob.herring@linaro.org>
Date: Wed, 14 May 2014 14:15:20 -0500
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Subject: Re: [Qemu-devel] [PATCH 6/7] arm/virt: enable PSCI emulation
	support for system emulation
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To: Peter Maydell <peter.maydell@linaro.org>, Pranavkumar Sawargaonkar <pranavkumar@linaro.org>
Cc: Rob Herring <robherring2@gmail.com>, QEMU Developers <qemu-devel@nongnu.org>, Christoffer Dall <christoffer.dall@linaro.org>

On Wed, May 14, 2014 at 12:51 PM, Peter Maydell
<peter.maydell@linaro.org> wrote:
> On 5 May 2014 17:00, Rob Herring <robherring2@gmail.com> wrote:
>> From: Rob Herring <rob.herring@linaro.org>
>>
>> Now that we have PSCI emulation, enable it for the virt platform.
>> This simplifies the virt machine a bit now that PSCI and SMP no longer
>> need to be KVM only features.

[...]

>> +    qemu_fdt_add_subnode(fdt, "/psci");
>> +    qemu_fdt_setprop_string(fdt, "/psci", "method", "hvc");
>> +    if (kvm_enabled() && !kvm_check_extension(kvm_state, KVM_CAP_ARM_PSCI_0_2)) {
>> +        qemu_fdt_setprop_string(fdt, "/psci", "compatible", "arm,psci");
>> +    } else {
>> +        const char compat[] = "arm,psci-0.2\0arm,psci";
>> +        qemu_fdt_setprop(fdt, "/psci", "compatible", compat, sizeof(compat));
>>      }
>
> My suggestion to Pranav was that we abstract away the "which PSCI
> version?" decision into a field in ARMCPU, in which case we can
> just have TCG always set it to 0.2. So some of this logic
> will get a little simpler on rebase.

You can't. You have to support both because you don't know what the
kernel supports. An old kernel will only support arm,psci.

Rob