(2012/04/12 9:06), Bjorn Helgaas wrote:
On Wed, Apr 11, 2012 at 9:34 AM, Jiang Liu<liuj97@xxxxxxxxx> wrote:
On 04/11/2012 08:05 PM, Kenji Kaneshige wrote:
(2012/04/11 13:02), Bjorn Helgaas wrote:
On Tue, Apr 10, 2012 at 6:10 PM, Jiang Liu<liuj97@xxxxxxxxx> wrote:
This patchset enhance pci_root driver to update MMCFG information when
hot-plugging PCI root bridges. It applies to Yinghai's tree at
git://git.kernel.org/pub/scm/linux/kernel/git/yinghai/linux-yinghai.git for-pci-root-bus-hotplug
The second patch is based on Taku Izumi work with some enhancements to
correctly handle PCI host bridges without _CBA method.
I'm sorry I won't have time to really review these for a couple weeks.
It always seemed wrong to me that we parse MCFG and set things up
before we even look at PNP0A03/PNP0A08 devices. It would make more
sense to me to have something in acpi_pci_root_add() to set up
MMCONFIG using _CBA if available, and falling back to parsing MCFG if
it's not.
I think your idea could make the code (design) much cleaner.
Do you have any other reason why you think "It always seemed
wrong..."?
The current scheme is just an ugly design. Does I need more reasons? :)
Ok, I just wanted to know if I'm missing anything we need to
take into account when re-factoring the code.
By the way, the following code makes me think there could be
some hardwares that need a fixup using mmconfig access before
scanning the PCI tree. If this is the case, we would need
something to enable early mmconfig initialization for those
hardwares.
static __init int pci_arch_init(void)
{
...
if (!(pci_probe & PCI_PROBE_NOEARLY))
pci_mmcfg_early_init();
Regards,
Kenji Kaneshige
Yeah, that may lead to a cleaner design.
But there are still some special cases, such as:
1) ACPI subsystem is disabled by kernel boot options, so we can't rely
on the ACPI pci_root driver to initialize the MMCFG.
I don't think it's a requirement to make everything work with
"acpi=off". On a system with ACPI, running with "acpi=off" is just a
kludge and if things work at all, it's only because we're very lucky.
2) Some PCI host bridges are not reported by the ACPI namespace. My partner
has observed a system which doesn't report the host bridges embedded in the
NHM-EX processors.
I don't think it's a requirement for Linux to use PCI devices behind
unreported host bridges. I'd like to pick a date and say "after BIOS
date X, we will no longer blindly probe for these unreported host
bridges."
Bjorn
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