linux-kernel - Re: [Xen-devel] [PATCH 1/3] PAD helper for native and paravirt platform

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Message-ID: <20120219182339.GA11882@phenom.dumpdata.com>
Date:	Sun, 19 Feb 2012 13:23:39 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	"Liu, Jinsong" <jinsong.liu@...el.com>
Cc:	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Kernel development list <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 1/3] PAD helper for native and paravirt
 platform

> >>> +struct pv_pad_ops {
> >>> +	int (*acpi_pad_init)(void);
> >>> +	void (*acpi_pad_exit)(void);
> >>> +};
> >>> +
> > 
> > Looking at this a bit closer I am not sure why you choose the paravirt
> > interface for this? There is another one - the x86 that could have
> > been 
> > choosen. Or introduce a new one that is specific to ACPI.
> > 
> > I am curious - what was the reason for using the paravirt interface?
> > I understand it does get the job done, but it seems a bit overkill
> > when something simple could have been used?
> > 
> 
> It uses paravirt interface to avoid some code like 'xen_...' in native code path (acpi_pad.c).
> I'm not quite sure what does 'x86' here mean? Adding 2 fields (acpi_pad_init/exit) in arch/x86/xen/enlighten.c --> xen_cpu_ops? seems it's much simpler.

arch/x86/include/asm/x86_init.h

But before you go that way let me ask you another question - can ACPI PAD
be used on ARM or IA64? If so, wouldn't this fail compilation as this pvops
structure is not defined on IA64?

The other thing I am not comfortable about is that the pvops structure
are used for low-level code. Not for higher up, like ACPI. For that another
structure seems more prudent. Perhaps something like the x86 one, but specific
to ACPI?
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