linux-kernel - RE: [Xen-devel] [PATCH 1/2] Xen acpi pad implement

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Date:	Tue, 30 Oct 2012 15:18:59 +0000
From:	"Liu, Jinsong" <jinsong.liu@...el.com>
To:	Konrad Rzeszutek Wilk <konrad@...nel.org>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jan Beulich <jbeulich@...e.com>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>
Subject: RE: [Xen-devel] [PATCH 1/2] Xen acpi pad implement

Konrad Rzeszutek Wilk wrote:
>>> +config XEN_ACPI_PAD_STUB
>>> +	bool
>>> +	depends on XEN_DOM0 && X86_64 && ACPI
>>> +	default n
>>> +
>> 
>> This Kconfig is pointless, if CONFIG_XEN_ACPI_PAD_STUB = n, native
>> pad would successfully registerred, and then mwait #UD (we would
>> revert df88b2d96e36d9a9e325bfcd12eb45671cbbc937, right?). So xen
>> stub logic should unconditionally built-in kernel.   
> 
> 
> Potentially. Keep in mind that there is no need to built this if the
> kernel is not built with ACPI.

Sure, 'obj-$(CONFIG_XEN_DOM0) +=' is enough.
(XEN_DOM0 depends on ACPI).

>>> +subsys_initcall(xen_acpi_pad_stub_init);
>> 
>> I'm still confused. In this way there are xen-acpi-pad-stub.c and
>> xen-acpi-pad.c, and you want to let xen-acpi-pad loaded as module,
>> right? how can xen-acpi-pad logic work when it was insmoded?  
> 
> Via the register/unregister calls that this provides? Or does ACPI bus
> drivers get immediately called once the call acpi_bus_register_driver?

But when xen stub driver registerred, real xen pad ops has not been hooked to stub ops.

> 
> Or can one 'poke' the 'add' and 'remove' calls so that once the "true"
> PAD driver is loaded it will restart the ops->add call?

I think we'd better not to use xen pad stub approach. Technically it's complicated, say, how to match xen_acpi_pad driver w/ pad device? when and how to invoke .add method? how to avoid native pad loading risk? etc. I didn't find its obivous advantages, so how about keep simpler approach?

Thanks,
Jinsong
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