linux-kernel - Re: [PATCH 0/5] ACPI / scan: Make it possible to use the container hotplug with other scan handlers

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Date:	Thu, 13 Jun 2013 15:28:59 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Luck, Tony" <tony.luck@...el.com>, Aaron Lu <aaron.lu@...el.com>
Subject: Re: [PATCH 0/5] ACPI / scan: Make it possible to use the container
 hotplug with other scan handlers

On Thu, 2013-06-13 at 01:23 +0200, Rafael J. Wysocki wrote:
> Hi All,
> 
> It turns out that some BIOSes add container device IDs as _CIDs to device
> object that in principle may be matched against the other scan handlers (or
> ACPI drivers, but that's not a problem, because the container scan handler
> can co-exist with an ACPI driver).  That's why our recent fix for an issue
> related to the ACPI video driver had to be reverted right before -rc5.

I am familiar with this firmware, although I no longer have access to
the systems.  An SBA device object has _HID with an HP-specific PNPID
and _CID with a generic container PNPID.  The _HID allows an OS with the
HP SBA driver (which recognizes the _HID) to enable the SBA's I/O TLB
functionality, while the _CID allows an OS without the HP SBA driver to
boot-up by treating this SBA as a container.  The _CID is needed because
some OS skips scanning underneath when it finds an unrecognized object.

> Although I submitted an alternative fix for that bug, I think the problem
> with the container scan handler possibly matching devices already having
> some other scan handlers attached needs addressing, because we may need to
> use the container hotplug profile for those devices.  The following patch
> series is supposed to address it.

When the HP SBA driver is bound to the SBA object, this driver needs to
handle a hotplug request when it is supported.  This is because the I/O
TLB functionality requires its hot-delete operation as well.  The
container scan handler can be used only when this driver is bound to the
SBA object as a container and therefore its I/O TLB functionality is not
used. 

> [1/5] ACPI / scan: Do not bind ACPI drivers to objects with scan handlers
>    (this version shouldn't break the Tony's IA64 HP box the previous one broke)
> [2/5] ACPI / scan: Separate hotplug profiles from scan handlers
> [3/5] ACPI / scan: Add hotplug profile pointer to struct acpi_device
> [4/5] ACPI / scan: Use container hotplug profile for matching device objects
> [5/5] ACPI / ia64 / sba_iommu: Use ACPI scan handler for discovery
> 
> Patches [1-4/5] were run on my Toshiba test box and didn't break it, but it
> really doesn't do any ACPI hotplug notifications.
> 
> Patch [5/5] is kind of additional, but it wouldn't work correctly without the
> previous ones (to be honest, I haven't tried to compile it yet, but here it
> goes for completness).

I think we only need patch [5/5] to address the problem.  We have
enhanced the match function of scan handlers to match a proper driver
with respect to their priority order, i.e. matching with _HID first and
then with _CIDs.  Patch [5/5] should assure that the HP SBA driver is
bound to an SBA object when this driver is configured to the kernel.

Thanks,
-Toshi

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