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From: Bjorn Helgaas <bhelgaas@google.com>
To: Jiang Liu <liuj97@gmail.com>
Cc: Jiang Liu <jiang.liu@huawei.com>,
	linux-pci@vger.kernel.org, Yinghai Lu <yinghai@kernel.org>
Subject: Re: [PATCH 1/2] PCI: introduce root bridge hotplug safe interfaces to walk root buses
Date: Tue, 18 Sep 2012 15:39:19 -0600	[thread overview]
Message-ID: <CAErSpo5QwebVypZK21R9_mXaWic0NJqMPzx8vd-FVfTDq9Ui4Q@mail.gmail.com> (raw)
In-Reply-To: <CAErSpo5uj9YwxjZweoLDsrx11S5NjCFwPeNfROsKySr1dTOjqQ@mail.gmail.com>

On Mon, Sep 17, 2012 at 10:24 AM, Bjorn Helgaas <bhelgaas@google.com> wrote:
> On Mon, Sep 17, 2012 at 9:55 AM, Jiang Liu <liuj97@gmail.com> wrote:
>> On 09/14/2012 01:40 AM, Bjorn Helgaas wrote:
>>> On Thu, Sep 13, 2012 at 10:00 AM, Jiang Liu <liuj97@gmail.com> wrote:
>>>> This patch introduces two root bridge hotplug safe interfaces to walk
>>>> all root buses. Function pci_get_root_buses() takes a snopshot of the
>>>> pci_root_buses list and holds a reference count to each root buses.
>>>> pci_{get|put}_root_buses are used to replace hotplug unsafe interface
>>>> pci_find_next_bus().
>>>
>>> Honestly, I think the whole idea of walking these lists is wrong, and
>>> adding safer interfaces just perpetuates the idea that it's OK to walk
>>> them.
>>>
>>> We should be doing the setup in the device add path instead.  I know
>>> we have other issues with that in some cases, but I'd like to at least
>>> move in that direction.
>>>
>>> For example, sba_init() is a problem because it's an ACPI driver, and
>>> we currently enumerate PCI devices before binding most ACPI drivers.
>>> That's broken -- in that particular case, there's an HWP0001 IOMMU
>>> device that encloses the PNP0A03 PCI host bridge.  Currently we bind
>>> the PNP0A03 driver first, enumerate the PCI devices below it, then
>>> bind the HWP0001 driver (sba_init).  Obviously that's backwards and
>>> the HWP0001 driver should have been bound first, then the PNP0A03
>>> driver.  But I don't think we're ready to make that shift yet (though
>>> it'd be nice if somebody were working on it).
>> I remember there were some discussions on the mail list above the divergence
>> between boot and hotplug paths. But it's a little hard for me to work on
>> this, I only have experience with PCI on IA64 and x86:(
>>
>>>
>>> I wonder if we could add some kind of iterator that does the list
>>> traversals in the PCI core and calls a callback for every device?  I
>>> think that would work for sba_init(), but I don't know about the
>>> others.  This would still be ugly in that the iterator would have to
>>> hold some sort of hotplug lock while doing for_each_pci_dev() and the
>>> callers, e.g., sba_init(), are not solving the problem for hot-added
>>> devices, but at least the locking would be in the core and the drivers
>>> would stop depending on the lists themselves.
>
>> I will try the iterator first, hope we could find a solution here.
>
> A plain iterator only handles devices that already exist.  But I
> wonder if it would work to have an interface like "call this callback
> for every device that exists already *and* for every device that's
> hot-added in the future."  The bus notifiers are close to this, e.g.,
> "bus_register_notifier(&pci_bus_type, ...)" handles this for hot-added
> devices.  A little glue around it could take care of doing it for
> already-existing devices as well.

BTW, while reviewing Yinghai's vga patch, I found a case in
vga_arb_device_init() that does exactly this: registers a notifier to
catch future hot-added devices, then calls the notifier "add" function
for every existing device.  So that's another place that could use
something like this.

  reply	other threads:[~2012-09-18 21:39 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-08-07 16:10 [RFC PATCH v1 00/22] introduce PCI bus lock to serialize PCI hotplug operations Jiang Liu
2012-08-07 16:10 ` [RFC PATCH v1 01/22] PCI: use pci_get_domain_bus_and_slot() to avoid race conditions Jiang Liu
2012-09-11 22:00   ` Bjorn Helgaas
2012-09-12  8:37     ` Jiang Liu
2012-08-07 16:10 ` [RFC PATCH v1 02/22] PCI: trivial cleanups for drivers/pci/remove.c Jiang Liu
2012-09-11 22:03   ` Bjorn Helgaas
2012-09-12  8:50     ` Jiang Liu
2012-08-07 16:10 ` [RFC PATCH v1 03/22] PCI: change PCI device management code to better follow device model Jiang Liu
2012-09-11 22:03   ` Bjorn Helgaas
2012-08-07 16:10 ` [RFC PATCH v1 04/22] PCI: split PCI bus device registration into two stages Jiang Liu
2012-08-07 16:10 ` [RFC PATCH v1 05/22] PCI: introduce pci_bus_{get|put}() to manage PCI bus reference count Jiang Liu
2012-08-07 16:10 ` [RFC PATCH v1 06/22] PCI: use a global lock to serialize PCI root bridge hotplug operations Jiang Liu
2012-09-11 22:57   ` Bjorn Helgaas
2012-09-12 15:42     ` Jiang Liu
2012-09-12 16:51       ` Bjorn Helgaas
2012-09-13 16:00         ` [PATCH 1/2] PCI: introduce root bridge hotplug safe interfaces to walk root buses Jiang Liu
2012-09-13 17:40           ` Bjorn Helgaas
2012-09-17 15:55             ` Jiang Liu
2012-09-17 16:24               ` Bjorn Helgaas
2012-09-18 21:39                 ` Bjorn Helgaas [this message]
2012-09-21 16:07                   ` [PATCH v4] PCI: introduce two interfaces to walk PCI buses Jiang Liu
2012-09-26 20:14                     ` Bjorn Helgaas
2012-09-13 16:00         ` [PATCH 2/2] PCI: remove host bridge hotplug unsafe interface pci_get_next_bus() Jiang Liu
2012-09-17 15:51         ` [RFC PATCH v1 06/22] PCI: use a global lock to serialize PCI root bridge hotplug operations Jiang Liu
2012-09-20 18:49         ` Paul E. McKenney
2012-08-07 16:10 ` [RFC PATCH v1 07/22] PCI: introduce PCI bus lock to serialize PCI " Jiang Liu
2012-09-11 23:24   ` Bjorn Helgaas
2012-08-07 16:10 ` [RFC PATCH v1 08/22] PCI: introduce hotplug safe search interfaces for PCI bus/device Jiang Liu
2012-08-07 16:10 ` [RFC PATCH v1 09/22] PCI: enhance PCI probe logic to support PCI bus lock mechanism Jiang Liu
2012-08-07 16:10 ` [RFC PATCH v1 10/22] PCI: enhance PCI bus specific " Jiang Liu
2012-08-07 16:10 ` [RFC PATCH v1 11/22] PCI: enhance PCI resource assignment " Jiang Liu
2012-08-07 16:10 ` [RFC PATCH v1 12/22] PCI: enhance PCI remove " Jiang Liu
2012-08-07 16:10 ` [RFC PATCH v1 13/22] PCI: make each PCI device hold a reference to its parent PCI bus Jiang Liu
2012-08-07 16:10 ` [RFC PATCH v1 14/22] PCI/sysfs: use PCI bus lock to avoid race conditions Jiang Liu
2012-08-07 16:10 ` [RFC PATCH v1 15/22] PCI/eeepc: " Jiang Liu
2012-09-11 23:18   ` Bjorn Helgaas
2012-09-12 14:24     ` [PATCH] eeepc-laptop: fix device reference count leakage in eeepc_rfkill_hotplug() Jiang Liu
2012-09-12 19:59       ` Bjorn Helgaas
2012-08-07 16:10 ` [RFC PATCH v1 16/22] PCI/asus-wmi: use PCI bus lock to avoid race conditions Jiang Liu
2012-08-07 16:10 ` [RFC PATCH v1 17/22] PCI/pciehp: " Jiang Liu
2012-08-07 16:10 ` [RFC PATCH v1 18/22] PCI/acpiphp: " Jiang Liu
2012-08-07 16:10 ` [RFC PATCH v1 19/22] PCI/x86: enable PCI bus lock mechanism for x86 platforms Jiang Liu
2012-09-11 23:22   ` Bjorn Helgaas
2012-09-12  9:56     ` Jiang Liu
2012-08-07 16:11 ` [RFC PATCH v1 20/22] PCI/IA64: enable PCI bus lock mechanism for IA64 platforms Jiang Liu
2012-08-07 16:11 ` [RFC PATCH v1 21/22] PCI: cleanups for PCI bus lock implementation Jiang Liu
2012-09-11 23:21   ` Bjorn Helgaas
2012-09-12  8:58     ` Jiang Liu
2012-08-07 16:11 ` [RFC PATCH v1 22/22] PCI: unexport pci_root_buses Jiang Liu
2012-08-07 18:11 ` [RFC PATCH v1 00/22] introduce PCI bus lock to serialize PCI hotplug operations Don Dutile
2012-08-08 15:49   ` Jiang Liu

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