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Date: Wed, 18 Mar 2009 17:29:23 +0900
From: Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>
To: Alex Chiang <achiang@...com>
CC: jbarnes@...tuousgeek.org, linux-pci@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 05/11] PCI: beef up pci_do_scan_bus()
Alex Chiang wrote:
> Hello Kenji-san,
>
> * Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>:
>> Alex Chiang wrote:
>>> I hadn't gotten around to verifying/fixing existing callers of
>>> pci_do_scan_bus yet. I was focusing on the core first.
>>>
>>> There aren't too many callers, but unfortunately, I don't have
>>> any hardware that actually uses the existing drivers.
>>>
>>> I seem to recall that your machines support shpchp. Would you
>>> mind testing this patch and telling me if your machine still
>>> behaves properly?
>>>
>> I have machines that support shpchp. But unfortunately I don't
>> have any adapter card that contains bridge, which is needed to
>> test your change.
>
> You're right.
>
> The more I think about it though, the more I think that even
> without the below patch to clean up the callers of
> pci_do_scan_bus, we should be ok, because:
>
> - all the old code (which I removed below) existed
> because the old PCI core would refuse to scan PCI buses
> that had already been discovered
>
> - that meant that it would never descend past a known
> bridge to try and find new child bridges
>
> - that meant that hotplug drivers had to manually
> discover new bridges and add them, essentially
> duplicating functionality in pci_scan_bridge
>
> This patch series allows the PCI core to scan existing bridges
> and descend down into the children every time, looking for new
> bridges and devices, so all the code in shpchp, cpcihp, and other
> callers of pci_do_scan_bus shouldn't be necessary anymore.
>
> Also, if we do add new bridges once manually in shpchp, and then
> call the new pci_do_scan_bus again, we will _not_ add devices
> twice because the core should check each bridge and device for
> struct pci_dev.is_added.
>
> So anyway, I think that cleaning up the callers of
> pci_do_scan_bus is a good idea, but multiple calls to the
> interface definitely should not result in problems. If they do,
> then that's a bug in my patch series.
>
I'm sorry, but I didn't have enough time to try your patch on
my environment. So I'm still just looking at the code.
I looked at shpchp_configure_device() from the view point of
bridge hot-add. I think it is broken regardless of your change
because it calls pci_bus_add_devices() (through pci_do_scan_bus)
before assigning resources. So I think it must be changed
regardless of your change. But it's a little difficult for me
because I don't have any test environment as I mentioned before.
But I'm still worrying about your change against pci_do_scan_bus().
Without your change, pci_do_scan_bus() scans child buses and add
devices without assigning resources. I guess that it means existing
callers of pci_do_scan_bus() have some mechanism to assign resource
by theirselves and they don't expect pci_do_scan_bus() assigns
resources.
By the way, I have one question about rescan. Please suppose that
we enable the bridge(B) and its children using rescan interface
in the picture below.
|
-------------------------------------- parent bus
| |
bridge(A) bridge(B)
(working) (Not working)
| |
------------- -------------
| | | |
dev dev dev dev
(working) (working) (Not working)
In this case, your rescan mechanism calls pci_do_scan_bus() for
parent bus, and pci_do_scan_bus() calls pci_bus_assign_resources()
for parent bus. My question is, does pci_bus_assign_resources() do
nothing against bridge(A) that is currently working? I guess
pci_bus_assign_resources() would update some registers of bridge(A)
and it would breaks currently working devices.
Thanks,
Kenji Kaneshige
>>> I looked at shpchp_configure_device and I think that simply
>>> scanning the device's parent bus should work.
>>>
>> Ok, I'll try it.
>
> I set up a git tree to make it easier to test:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/achiang/pci-hotplug.git
>
> The 'test-20090313' branch contains all the latest fixes to
> enable this patch series. It does not contain the patch below, so
> you will have to apply it by hand.
>
> Thanks for testing!
>
> /ac
>
>>> Thanks.
>>>
>>> /ac
>>>
>>> diff --git a/drivers/pci/hotplug/shpchp_pci.c b/drivers/pci/hotplug/shpchp_pci.c
>>> index aa315e5..7e8457b 100644
>>> --- a/drivers/pci/hotplug/shpchp_pci.c
>>> +++ b/drivers/pci/hotplug/shpchp_pci.c
>>> @@ -110,11 +110,7 @@ int __ref shpchp_configure_device(struct slot *p_slot)
>>> return -EINVAL;
>>> }
>>>
>>> - num = pci_scan_slot(parent, PCI_DEVFN(p_slot->device, 0));
>>> - if (num == 0) {
>>> - ctrl_err(ctrl, "No new device found\n");
>>> - return -ENODEV;
>>> - }
>>> + pci_do_scan_bus(parent);
>>>
>>> for (fn = 0; fn < 8; fn++) {
>>> dev = pci_get_slot(parent, PCI_DEVFN(p_slot->device, fn));
>>> @@ -126,40 +122,10 @@ int __ref shpchp_configure_device(struct slot *p_slot)
>>> pci_dev_put(dev);
>>> continue;
>>> }
>>> - if ((dev->hdr_type == PCI_HEADER_TYPE_BRIDGE) ||
>>> - (dev->hdr_type == PCI_HEADER_TYPE_CARDBUS)) {
>>> - /* Find an unused bus number for the new bridge */
>>> - struct pci_bus *child;
>>> - unsigned char busnr, start = parent->secondary;
>>> - unsigned char end = parent->subordinate;
>>> - for (busnr = start; busnr <= end; busnr++) {
>>> - if (!pci_find_bus(pci_domain_nr(parent),
>>> - busnr))
>>> - break;
>>> - }
>>> - if (busnr > end) {
>>> - ctrl_err(ctrl,
>>> - "No free bus for hot-added bridge\n");
>>> - pci_dev_put(dev);
>>> - continue;
>>> - }
>>> - child = pci_add_new_bus(parent, dev, busnr);
>>> - if (!child) {
>>> - ctrl_err(ctrl, "Cannot add new bus for %s\n",
>>> - pci_name(dev));
>>> - pci_dev_put(dev);
>>> - continue;
>>> - }
>>> - child->subordinate = pci_do_scan_bus(child);
>>> - pci_bus_size_bridges(child);
>>> - }
>>> program_fw_provided_values(dev);
>>> pci_dev_put(dev);
>>> }
>>>
>>> - pci_bus_assign_resources(parent);
>>> - pci_bus_add_devices(parent);
>>> - pci_enable_bridges(parent);
>>> return 0;
>>> }
>>>
>>>
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