linux-kernel - Re: [Xen-devel] [PATCH 1/2] RFC: Prepare PAD for native and xen platform

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Date:	Mon, 26 Mar 2012 12:48:35 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	"Liu, Jinsong" <jinsong.liu@...el.com>
Cc:	"Brown, Len" <len.brown@...el.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"keir.xen@...il.com" <keir.xen@...il.com>,
	Jan Beulich <jbeulich@...e.com>,
	"Li, Shaohua" <shaohua.li@...el.com>,
	"lenb@...nel.org" <lenb@...nel.org>
Subject: Re: [Xen-devel] [PATCH 1/2] RFC: Prepare PAD for native and	xen
 platform

> > Compare approaches:
> > 
> > 1. xen overwritten approach (patches V2, x86_init, osl approach)
> >     Pros:
> >         a little simpler code
> >     Cons:
> >         1). specific to xen, cannot extend to other virt platform;
> >         2). need to change natvie acpi_pad as modular;
> > 
> > 2. paravirt interface approach (original patches V1)
> >     Pros:
> >         1). standard hypervisor-agnostic interface (USENIX conference
> >         2006), can easily hook to Xen/lguest/... on demand; 2). arch
> >         independent; 3). no need to change native acpi_pad as
> >     non-modular; Cons:
> >         a little complicated code, and code patching is some
> > overkilled for this case (but no harm); 
> > 
> > (BTW, in the future we need add more and more pv ops, like pv_pm_ops,
> > pv_cpu_hotplug_ops, pv_mem_hotplug_ops, etc. So how about add a
> > pv_misc_ops template to handle them all? seems it's a common issue).  
> > 

I think (and you probabaly have a better idea) is that the maintainer of 
drivers/acpi/* is not very open to adding in code that only benefits Xen.

If it benefits other architectures (say ARM) then adding in hooks there
(in osl for example) makes sense - but I am not sure if ARM has a form
of _PUR code/calls it needs to do.

So with that in mind, neither of those options seems proper - as all of them
depend on changing something in drivers/acpi/*.

I've one or two suggestions of what could be done to still make this
work, but I need you to first see what happens if the native acpi_pad
runs under Xen with the latest upstream code (along with three patches
that are in a BZ I pointed you too). 
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