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

[Igor Mammedov <imammedo@redhat.com>]

On Tue, 20 Jan 2015 16:08:09 +0000
Peter Maydell <peter.maydell@linaro.org> wrote:

> On 20 January 2015 at 15:59, Igor Mammedov <imammedo@redhat.com> wrote:
> > On Tue, 20 Jan 2015 15:34:23 +0000
> > Peter Maydell <peter.maydell@linaro.org> wrote:
> >
> >> On 20 January 2015 at 15:22, Igor Mammedov <imammedo@redhat.com> 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