linux-kernel - Re: [PATCH v3 00/22] PCI: Iterate pci host bridge instead of pci root bus

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Date:	Wed, 6 Feb 2013 10:45:16 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Mauro Carvalho Chehab <mchehab@...hat.com>
Cc:	Yinghai Lu <yinghai@...nel.org>, Jiang Liu <jiang.liu@...wei.com>,
	Tony Luck <tony.luck@...el.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Taku Izumi <izumi.taku@...fujitsu.com>,
	Toshi Kani <toshi.kani@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-pci@...r.kernel.org, Russell King <linux@....linux.org.uk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 00/22] PCI: Iterate pci host bridge instead of pci root bus

On Wed, Feb 6, 2013 at 1:53 AM, Mauro Carvalho Chehab
<mchehab@...hat.com> wrote:
> Em Tue, 5 Feb 2013 16:47:10 -0800
> Yinghai Lu <yinghai@...nel.org> escreveu:
>
>> On Tue, Feb 5, 2013 at 4:19 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
>> >
>> > Maybe.  I'd rather not introduce for_each_pci_host_bridge() at all, if
>> > we can avoid it.  Every place it's used is a place we have to audit to
>> > make sure it's safe.  I think your audit above is correct and
>> > complete, but it relies on way too much architecture knowledge.  It's
>> > better if we can deduce correctness without knowing which arches
>> > support hotplug and which CPUs support EDAC.
>> >
>> > As soon as for_each_pci_host_bridge() is in the tree, those uses can
>> > be copied to even more places.  It's a macro, so it's usable by any
>> > module, even out-of-tree ones that we'll never see and can't fix.  So
>> > we won't really have a good way to deprecate and remove it.
>>
>> Now we only have two references in modules.
>>
>> drivers/edac/i7core_edac.c:     for_each_pci_host_bridge(host_bridge) {
>> drivers/pci/hotplug/sgi_hotplug.c:      for_each_pci_host_bridge(host_bridge) {
>>
>> for the sgi_hotplug.c, it should be same problem that have for acpiphp
>> and pciehp.
>> need to make it support pci host bridge hotplug anyway.
>>
>> for edac, we need to check Mauro about their plan.
>
> The i7core_pci_lastbus() code at i7core_edac is there to make it work
> with some Nehalem/Nehalem-EP machines that hide the memory controller's
> PCI ID by using an artificially low last bus.

I don't really understand how this helps.  An example would probably
make it clearer.

i7core_edac.c has some very creative use of PCI infrastructure.
Normally a driver has a pci_device_id table that identifies the
vendor/device IDs of the devices it cares about, and the driver's
.probe() method is called for every matching device.

But i7core_edac only has two entries in its id_table.  When we find a
device that matches one of those two entries, we call i7core_probe(),
which then gropes around for all the *other* devices related to that
original one.  This is a bit messy.

I'd like it a lot better if the device IDs in
pci_dev_descr_i7core_nehalem[], pci_dev_descr_lynnfield[], etc., were
just in the pci_device_id table directly.  Then i7core_probe() would
be called directly for every device you care about, and you could sort
them out there.  That should work without any need for
pci_get_device(), i7core_pci_lastbus(), etc.

Bjorn
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