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Re: [Qemu-ppc] [PATCH v5 04/36] ppc/xive: introduce the XiveRouter model

From: David Gibson
Subject: Re: [Qemu-ppc] [PATCH v5 04/36] ppc/xive: introduce the XiveRouter model
Date: Mon, 26 Nov 2018 16:44:29 +1100
User-agent: Mutt/1.10.1 (2018-07-13)

On Fri, Nov 23, 2018 at 11:28:24AM +0100, Cédric Le Goater wrote:
> On 11/23/18 2:10 AM, David Gibson wrote:
> > On Thu, Nov 22, 2018 at 05:50:07PM +1100, Benjamin Herrenschmidt wrote:
> >> On Thu, 2018-11-22 at 15:44 +1100, David Gibson wrote:
> >>>
> >>> Sorry, didn't think of this in my first reply.
> >>>
> >>> 1) Does the hardware ever actually write back to the EAS?  I know it
> >>> does for the END, but it's not clear why it would need to for the
> >>> EAS.  If not, we don't need the setter.
> >>
> >> Nope, though the PAPR model will via hcalls
> > 
> > Right, bit AIUI the set_eas hook is about abstracting PAPR vs bare
> > metal details.  Since the hcall knows it's PAPR it can just update the
> > backing information for the EAS directly, and no need for an
> > abstracted hook.
> Indeed, the first versions of the XIVE patchset did not use such hooks, 
> but when discussed we said we wanted abstract methods for the router 
> to validate the overall XIVE model, which is useful for PowerNV. 
> We can change again and have the hcalls get/set directly in the EAT
> and ENDT. It would certainly simplify the sPAPR model.

I think that's the better approach.

> >>> 2) The signatures are a bit odd here.  For the setter, a value would
> >>> make sense than a (XiveEAS *), since it's just a word.  For the getter
> >>> you could return the EAS value directly rather than using a pointer -
> >>> there's already a valid bit in the EAS so you can construct a value
> >>> with that cleared if the lisn is out of bounds.
> >>
> > 

David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!

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