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SubjectRe: [PATCH v3 4/6] PCI/acpiphp: update ACPI hotplug slot information when PCI hotplug happens
On 01/10/2013 04:23 AM, Rafael J. Wysocki wrote:
> On Thursday, January 10, 2013 12:29:55 AM Jiang Liu wrote:
>> On 01/09/2013 08:04 AM, Rafael J. Wysocki wrote:
>>> On Wednesday, January 09, 2013 12:52:23 AM Jiang Liu wrote:
>>>> Currently the acpiphp driver fails to update hotplug slot information under
>>>> several conditions, such as:
>>>> 1) The bridge device is removed through /sys/bus/pci/devices/.../remove
>>>> 2) The bridge device is added/removed by PCI hotplug driver other than the
>>>> acpiphp driver itself. For example, if an IO expansion box with ACPI
>>>> hotplug slots available is hot-added by the pciehp driver, all ACPI
>>>> hotplug slots won't be discovered by the acpiphp driver.
>>>> update ACPI hotplug slot information when PCI hotplug event happens.
>>>> Signed-off-by: Jiang Liu <>
>>>> Signed-off-by: Yijing Wang <>
>>>> ---
>>>> drivers/pci/hotplug/acpiphp_glue.c | 62 ++++++++++++++++++++++++++++++++++--
>>>> 1 file changed, 60 insertions(+), 2 deletions(-)
>> snip
>>>> +static struct notifier_block acpi_pci_hp_notifier = {
>>>> + .notifier_call = &acpi_pci_hp_notify_fn,
>>>> +};
>>>> +
>>>> static struct acpi_pci_driver acpi_pci_hp_driver = {
>>>> .add = add_bridge,
>>>> .remove = remove_bridge,
>>>> @@ -1448,6 +1503,8 @@ int __init acpiphp_glue_init(void)
>>>> else
>>>> acpi_pci_register_driver(&acpi_pci_hp_driver);
>>>> + bus_register_notifier(&pci_bus_type, &acpi_pci_hp_notifier);
>>> Your previous patch adds a PCI bus notifier for a similar thing. Why are
>>> you adding another one here?
>> Hi Rafael,
>> The acpiphp driver could be built as a module, and this bus notifier
>> is used to setup/tear down ACPI based PCI hotplug controllers under a PCI bridge.
>> The previous patch is to add/remove PCI slots. The PCI slot and PCI hotplug
>> controller are related but different objects, so we use two notifiers to support
>> them all.
> I would be much happier if those notifiers were not needed. At least, I'm not
> sure why they need to be invoked by the driver core during device registration.
> In my opinion it would be much better if they were called only for the devices
> that might need them instead of all PCI devices.
Hi Rafael,
The whole thing seems a little complex, and I will try my best to explain
about it:)
Essentially a PCI slot is associated with a PCI bus, and a PCI bus is
associated with a host bridge or P2P bridge. When hot-adding/hot-removing a PCI bus,
we need to create/destroy PCI slots associated with it. So the pci_slot and acpiphp
drivers need to be notified when hot-adding/hot-removing a PCI bus.
But there's no common mechanism to get notified when PCI buses are being
hot-added/hot-removed. So my first implementation has introduced a dedicated notifier
chain for PCI bus addition/removal. Later with ongoing changes to the PCI core,
I found we could rely on the existing bus notification mechanism too, so that becomes
the current implementation.
I have a proposal to unify the process for boot time and hotplug as below:
1) Change pci_slot and acpiphp as built-in instead of modules.
2) Get rid of acpi_pci_driver for pci_slot and acpiphp driver.
3) Register some forms of callbacks to create/destroy hotplug controllers/slots
when creating/destroying PCI buses.
3.a) Rely on the bus notification mechanism to invoke callbacks. This solution is
simple, but with a little overhead
3.b) Introduce a dedicated notifier chain for PCI bus hot-adding/hot-removing.
This solution could get rid of the overhead, but with more code changes.
3.c) Invoke callbacks from acpi_bus_type->setup/cleanup. This solution could
only support ACPI based slots, such as pci_slot and acpiphp.
Any recommendations?

> Thanks,
> Rafael

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