linux-kernel - Re: [PATCH v2 1/7] ACPI: Add CONFIG_HOTPLUG

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Date:	Fri, 11 May 2012 01:43:15 +0800
From:	Jiang Liu <liuj97@...il.com>
To:	Toshi Kani <toshi.kani@...com>
CC:	lenb@...nel.org, linux-acpi@...r.kernel.org, bhelgaas@...gle.com,
	shuahkhan@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/7] ACPI: Add CONFIG_HOTPLUG_OST option

On 05/11/2012 01:26 AM, Toshi Kani wrote:
> On Fri, 2012-05-11 at 00:40 +0800, Jiang Liu wrote:
>> On 05/09/2012 04:12 AM, Toshi Kani wrote:
>>> Added CONFIG_ACPI_HOTPLUG_OPT option. When this config option is disabled,
>>> this patchset has no effect on the platform. This option is disabled by
>>> default. The dependency list assures consistent behavior among CPU, memory
>>> and container hotplug operations with regarding the _OST support.
>> Seems also need to enhance the acpiphp driver for PCI hotplug operations too.
>> acpiphp driver is also based on the ACPI device hotplug model.
> 
> Good question.  ACPI PCI hotplug is a legacy method, which is being
> replaced by PCI native hotplug.  I expect PCI native hotplug will be
> used for any platforms supporting PCI-E.  Since this _OST support is
> targeted for new platforms (as _OST is not supported on the current
> platforms), I thought that it would be prudent to avoid changing PCI
> hotplug code for this.
You are right, acpiphp is legacy method. But it may also be used to support
some cases which can't be supported by the pciehp driver.
For example, we have a PCIe system which needs to run acpiphp and pciehp
concurrently. The pciehp driver is used to manage hot-pluggable PCIe slot,
and the acpiphp driver is used to migrate downstream ports among virtual 
PCIe switches of an MR-IOV switch. It would be great if we could enable 
_OST for acpiphp too.

To be honest, our BIOS doesn't provide _OST for acpiphp yet, so we could
enhance acpiphp driver in future when a system really needing that feature
appears.

Thanks!
--gerry
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