linux-kernel - Re: [RFC PATCH v2 00/16] ACPI based system device hotplug framework

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Date:	Wed, 8 Aug 2012 09:27:07 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Jiang Liu <liuj97@...il.com>
Cc:	Toshi Kani <toshi.kani@...com>, Jiang Liu <jiang.liu@...wei.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	Wen Congyang <wency@...fujitsu.com>,
	Tang Chen <tangchen@...fujitsu.com>,
	Taku Izumi <izumi.taku@...fujitsu.com>,
	Tony Luck <tony.luck@...el.com>,
	Huang Ying <ying.huang@...el.com>,
	Bob Moore <robert.moore@...el.com>,
	Len Brown <lenb@...nel.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	linux-pci@...r.kernel.org
Subject: Re: [RFC PATCH v2 00/16] ACPI based system device hotplug framework

On Wed, Aug 8, 2012 at 8:44 AM, Jiang Liu <liuj97@...il.com> wrote:
> On 08/08/2012 07:38 AM, Toshi Kani wrote:

>> It is nice to see redundant ACPI namespace walks removed from the ACPI
>> drivers.  But why do you need to add a new enumerator to create the
>> acpihp_slot tree, in addition to the current acpi_device tree?  I'd
>> prefer hotplug features to be generally integrated into the current ACPI
>> core code and data structures, instead of adding a new layer on top of
>> it.
> The idea comes from PCI hotplug framework, which has an concepts of PCI
> hotplug slot and PCI device. For system device hotplug, we could follow
> the same model as PCI by abstracting control points as slots. By introducing
> of hotplug slot, we could:
>
> 1) Report all hotplug slots and slot's capabilities to user, no matter whether
> there are devices connecting to a slot. If we integrate hotplug functionality
> into current ACPI device tree, the slot (or device) is only visible when the
> connected devices are enabled.

In PCI, the idea of a slot is a pretty explicit -- you can look at the
capabilities of a bridge device and see whether it supports hot-add of
a device below it.  Is it the same way in ACPI?  My impression is that
it is not: there will be a parent ACPI device under which a new device
can be added, but you might not be able to tell by looking at the
parent device that hot-add is possible.  I thought the platform could
just give us a Notify event on the parent, asking us to rescan the
namespace below it and potentially discover new devices.
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