Re: [Qemu-devel] [PATCH 1/5] target-arm: Add ARM CPU feature parsing

[Greg Bellows]

On Tue, Jan 20, 2015 at 10:25 AM, Igor Mammedov <address@hidden> wrote:
> On Tue, 20 Jan 2015 16:08:09 +0000
> Peter Maydell <address@hidden> wrote:
>
>> On 20 January 2015 at 15:59, Igor Mammedov <address@hidden> wrote:
>> > On Tue, 20 Jan 2015 15:34:23 +0000
>> > Peter Maydell <address@hidden> wrote:
>> >
>> >> On 20 January 2015 at 15:22, Igor Mammedov <address@hidden> wrote:
>> >> > Please do not use legacy +-feature format and support only foo=val 
>> >> > format.
>> >> > Other targets have it only for to being able support legacy setups
>> >> > which use +- format.
>> >>
>> >> I thought this was the standard format for CPU features. Do you
>> >> have an example of a CPU feature being set using foo=val format?
>> > Currently on x86 we can use either legacy +foo1,-foo2,foo3 and
>> > in addition to it we ca use canonized format for generic properties
>> > like, foo1=on,foo2=off,foo3=on
>> >
>> > We try to move out of legacy format, so that it would be possible
>> > to reuse generic property parsing infrastructure like with any
>> > device object. That would allow to use -device/device_add for CPUs.
>>
>> -device/-device_add for CPUs is pretty fraught in the general
>> case because there's no obvious place to plug them and have
>> them be wired up properly.
> That depends on CPU of-cause, but we are close to having device_add
> working with x86 CPUs.
>
>> You'd need to use -global for CPU
>> properties, which is a nightmare...
> mine thoughts on it were that '-cpu type,feat...' would  eventually
> do conversion of features to global properties transparently for
> user using target specific cc->parse_features() callback. Which
> Greg could actually do here. We would happy to reuse it with x86 CPUs.
>
>>
>> Anyway, I'm not particularly attached to the exact command
>> line syntax we've used here -- I was just looking for "we have
>> a CPU property, and use the same syntax for specifying CPU
>> feature enable/disable that other CPUs do"...
> Then '-cpu arm_foo,featX=on/off' should do the job.
>
>
>>
>> -- PMM
>

For now I went with the "-cpu arm_foo,aarch64=off" approach so as to
not complicate it right now with adding full-blown CPU properties.