linux-kernel - Re: [PATCH 0/4] ACPI: kill acpi_pci_root

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Date:	Thu, 4 Oct 2012 15:46:39 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Len Brown <lenb@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH 0/4] ACPI: kill acpi_pci_root_start

On Thu, Oct 4, 2012 at 3:36 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> On Thursday 04 of October 2012 15:01:21 Yinghai Lu wrote:
>> during adding pci root bus hotplug, Bjorn found some unsafe searching
>> that caused by pci_bus_add_devices.
>
> Do you have a link to a description of that problem?

Maybe bjorn could expand it more.

>
>> pci devices are created during pci scan root, but until very late
>> acpi_pci_root_start call pci_bus_add_devices.
>
> So you mean that pci_bus_add_devices() is called too late, right?

yes.

>
>> To fill the gap, we need to move pci_bus_add_devices to acpi_pci_root_add
>> at first.
>>
>> but after we move that there, pci device will be added to device tree, and it
>> will try to bind with acpi devices that should be under acpi pci root,
>> but are not
>> created yet. because device_add for acpi_device for acpi pci root is done yet.
>> it still calling the .add in the acpi_driver aka acpi_pci_root_add.
>
> Quite obviously, we haven't walked the ACPI namespace below the host bridge
> object yet at that point.

yes.

>
>> So I want to hold the driver attach for pci root acpi devices, and
>> later attach it
>> until pci devices created.
>>
>> booting path, all acpi devices get created, and attach driver for them
>> one by one.
>
> I see.
>
> Your patches seem to affect all devices in the ACPI namespace added after
> boot, though, not only host bridges.

yes, but it still should be safe.

>
> And the problem seems to be that the scanning of the ACPI namespace and
> configuring the host bridge are kind of independent operations now.  What
> we should do, actually, seems to be something like this:
>
> (1) Configure the host bridge when discovered (i.e. do what the current
>     acpi_pci_root_add() does.
> (2) Parse the ACPI namespace under the host bridge (without binding ACPI
>     drivers to the struct acpi_device objects created in the process,
>     because they are known to correspond to PCI devices).
> (3) Run pci_bus_add_devices() for the bridge.
>
> in one routine.

problem is still there. if 1 still has acpi_pci_root_add and pci_acpi_scan_root
that scan pci devices. what is need is we need to bind 1 and 3 together.

or we could move pci_scan_root_scan from acpi_pci_root_add to
acpi_pci_root_start?
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