Re: handling cp15 state which isn't trivially exposed as a single register

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On Tue, 21 Aug 2012 09:35:21 +0200, Alexander Graf <agraf@xxxxxxx> wrote:
> On 21.08.2012, at 04:32, Rusty Russell <rusty.russell@xxxxxxxxxx> wrote:
> > Now, if Anthony and Avi lay down the law and say everyone is moving to a
> > new system, we'll move now.  For real: I want to see x86 patches.
> 
> So because x86 has a stable API today that works for them and that
> needs to be supported anyways we don't improve the non-x86 code? What
> an awesome argument. I should bring that one up next time I don't want
> to think about something.

It's not an improvement.  You want change, so we can unify.  But it
won't actually unify anything important, since x86 will not be unified.
Right?

> > Otherwise, we'll concentrate on stuff we know, and transition when
> > everyone else does.
> > 
> > And since that transition is likely to be painful and of no real
> > benefit, it might never happen.
> 
> That's exactly my point. Today you have the chance and could go with
> something generic, extensible.

Today?  No, you don't have what we need today.

> In fact, you basically reimplemented ONE_REG on top of the x86 MSR
> ioctls.

Not if you order your narrative in linear time.  You reimplemented MSR,
badly.  I copied MSR, and ignored ONE_REG altogether.

> So either try to work with everyone on a solution for everyone, rename the ioctls to something more generic, or invent new ones for you. But don't create another arm-one-reg api under the MSR code name.

We could easily rename ARM's MSR-style ioctls to sound generic.  We
could reserve the upper 6 bits of the index for an architecture tag so
everyone has their own namespace, or just bloat the index to 64 bits.

But will it be any more successful than ONE_REG?  What would we gain?

Are you going to be at KS/Plumbers?  Avi, you?  Because grand plans seem
to work badly over email.

Cheers,
Rusty.
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