linux-kernel - Re: [RFC PATCH v3 0/3] acpi: Introduce prepare

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Date:	Thu, 06 Dec 2012 19:25:18 -0700
From:	Toshi Kani <toshi.kani@...com>
To:	Jiang Liu <liuj97@...il.com>
Cc:	Hanjun Guo <guohanjun@...wei.com>,
	Vasilis Liaskovitis <vasilis.liaskovitis@...fitbricks.com>,
	linux-acpi@...r.kernel.org, isimatu.yasuaki@...fujitsu.com,
	wency@...fujitsu.com, rjw@...k.pl, lenb@...nel.org,
	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Tang Chen <tangchen@...fujitsu.com>,
	Liujiang <jiang.liu@...wei.com>, Huxinwei <huxinwei@...wei.com>
Subject: Re: [RFC PATCH v3 0/3] acpi: Introduce prepare_remove device
 operation

On Fri, 2012-12-07 at 00:47 +0800, Jiang Liu wrote:
> On 12/05/2012 07:23 AM, Toshi Kani wrote:
> > On Tue, 2012-12-04 at 17:16 +0800, Hanjun Guo wrote:
> >> On 2012/12/4 8:10, Toshi Kani wrote:
> >>> On Mon, 2012-12-03 at 12:25 +0800, Hanjun Guo wrote:
> >>>> On 2012/11/30 6:27, Toshi Kani wrote:
> >>>>> On Thu, 2012-11-29 at 12:48 +0800, Hanjun Guo wrote:
> >>>>>> On 2012/11/29 2:41, Toshi Kani wrote:
:
> >>>> The ACPI specification provides _EDL method to
> >>>> tell OS the eject device list, but still has no method to tell OS the add device
> >>>> list now.
> >>>
> >>> Yes, but I do not think the OS needs special handling for add...
> >>
> >> Hmm, how about trigger a hot add operation by OS ? we have eject interface for OS, but
> >> have no add interface now, do you think this feature is useful? If it is, I think OS
> >> should analyze the dependency first and tell the user.
> > 
> > The OS can eject an ACPI device because a target device is owned by the
> > OS (i.e. enabled).  For hot-add, a target ACPI device is not owned by
> > the OS (i.e. disabled).  Therefore, the OS is not supposed to change its
> > state.  So, I do not think we should support a hot-add operation by the
> > OS.
> We depends on the firmware to provide an interface to actually hot-add the device.
> The sequence is:
> 1) user trigger hot-add request by sysfs interfaces.
> 2) hotplug framework validates conditions for hot-adding (dependency)
> 3) hotplug framework invokes firmware interfaces to request a hot-adding operation.
> 4) firmware sends an ACPI notificaitons after powering on/initializing the device
> 5) OS adds the devices into running system.

Interesting...  In this sequence, I think FW must validate and check the
dependency before sending a SCI.  FW owns unassigned resources and is
responsible for the procedure necessary to enable resources on the
platform.  Such steps are basically platform-specific.  So, I do not
think the common OS code should step into such business.

Thanks,
-Toshi

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