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Date: Wed, 09 Jan 2013 21:19:17 +0100
From: "Rafael J. Wysocki" <rjw@...k.pl>
To: Jiang Liu <liuj97@...il.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>,
Jiang Liu <jiang.liu@...wei.com>,
Yijing Wang <wangyijing@...wei.com>,
linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH v3 3/6] ACPI/pci_slot: update PCI slot information when PCI hotplug event happens
On Thursday, January 10, 2013 12:58:25 AM Jiang Liu wrote:
> Hi Rafael,
> Thanks for your great efforts to review the patch.
>
> On 01/09/2013 08:01 AM, Rafael J. Wysocki wrote:
> > Hi,
> >
> > On Wednesday, January 09, 2013 12:52:22 AM Jiang Liu wrote:
> snip
> >>
> >> +static void acpi_pci_slot_notify_add(struct pci_dev *dev)
> >> +{
> >> + acpi_handle handle;
> >> + struct callback_args context;
> >> +
> >> + if (!dev->subordinate)
> >> + return;
> >> +
> >> + mutex_lock(&slot_list_lock);
> >> + handle = DEVICE_ACPI_HANDLE(&dev->dev);
> >> + context.root_handle = acpi_find_root_bridge_handle(dev);
> >
> > There's a patch under discussion that removes this function.
> >
> > Isn't there any other way to do this?
> I will try to find a way to get rid of calling acpi_find_root_bridge_handle,
> and it seems doable.
>
> >
> >> + if (handle && context.root_handle) {
> >> + context.pci_bus = dev->subordinate;
> >> + context.user_function = register_slot;
> >> + acpi_walk_namespace(ACPI_TYPE_DEVICE, handle, (u32)1,
> >
> > You can just pass 1 here I think. Does the compiler complain?
> Thanks for reminder, the (u32) is unnecessary.
>
> >
> >> + register_slot, NULL, &context, NULL);
> >> + }
> >> + mutex_unlock(&slot_list_lock);
> >> +}
> >> +
> >> +static void acpi_pci_slot_notify_del(struct pci_dev *dev)
> >> +{
> >> + struct acpi_pci_slot *slot, *tmp;
> >> + struct pci_bus *bus = dev->subordinate;
> >> +
> >> + if (!bus)
> >> + return;
> >> +
> >> + mutex_lock(&slot_list_lock);
> >> + list_for_each_entry_safe(slot, tmp, &slot_list, list)
> >> + if (slot->pci_slot && slot->pci_slot->bus == bus) {
> >> + list_del(&slot->list);
> >> + pci_destroy_slot(slot->pci_slot);
> >> + put_device(&bus->dev);
> >> + kfree(slot);
> >> + }
> >> + mutex_unlock(&slot_list_lock);
> >> +}
> >> +
> >> +static int acpi_pci_slot_notify_fn(struct notifier_block *nb,
> >> + unsigned long event, void *data)
> >> +{
> >> + struct device *dev = data;
> >> +
> >> + switch (event) {
> >> + case BUS_NOTIFY_ADD_DEVICE:
> >> + acpi_pci_slot_notify_add(to_pci_dev(dev));
> >> + break;
> >
> > Do I think correctly that this is going to be called for every PCI device
> > added to the system, even if it's not a bridge?
> You are right. Function acpi_pci_slot_notify_add() and acpi_pci_slot_notify_del()
> will check whether it's a bridge. If preferred, I will move the check up into
> acpi_pci_slot_notify_fn().
>
> >
> >> + case BUS_NOTIFY_DEL_DEVICE:
> >> + acpi_pci_slot_notify_del(to_pci_dev(dev));
> >> + break;
> >> + default:
> >> + return NOTIFY_DONE;
> >> + }
> >> +
> >> + return NOTIFY_OK;
> >> +}
> >> +
> >> +static struct notifier_block acpi_pci_slot_notifier = {
> >> + .notifier_call = &acpi_pci_slot_notify_fn,
> >> +};
> >> +
> >> static int __init
> >> acpi_pci_slot_init(void)
> >> {
> >> dmi_check_system(acpi_pci_slot_dmi_table);
> >> acpi_pci_register_driver(&acpi_pci_slot_driver);
> >> + bus_register_notifier(&pci_bus_type, &acpi_pci_slot_notifier);
> >
> > I wonder if/why this has to be so convoluted?
> >
> > We have found a PCI bridge in the ACPI namespace, so we've created a struct
> > acpi_device for it and we've walked the namespace below it already.
> >
> > Now we're creating a struct pci_dev for it and while registering it we're
> > going to walk the namespace below the bridge again to find and register its
> > slots and that is done indirectly from a bus type notifier.
> >
> > Why can't we enumerate the slots directly upfront?
> Do you mean to create the PCI slot devices when creating the ACPI devices?
> I think there are two factors prevent us from doing that.
> The first is that the ACPI pci_slot driver could be built as a module, so
> we can't call into it from the ACPI core.
I didn't say about calling the pci_slot driver from the ACPI core, but about
enumerating slots in a way suitable for consumption by the pci_slot driver
when it's ready.
That said I really don't see a value in having a modular pci_slot driver. It
is part of the hotplug infrastructure and should always be presend for this
reason, so we don't need to worry about the "pci_slot driver not present" case.
> The second reason is that the PCI slot is associated with a PCI bus, and the
> bus is only available until the PCI device has been created.
I suppose you mean "after"? [I'm not sure if I agree with that, but whatever.]
We know which devices have slots before that happens, though.
Thanks,
Rafael
--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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