On 04/16/2012 12:09 PM, Jiang Liu wrote:
Hi Don,
Thanks for your comments and please refer to inline comments below.
Thanks for the info below; couple quick replies below.. - Don
On 04/16/2012 11:30 PM, Don Dutile wrote:
On 04/13/2012 10:33 AM, Jiang Liu wrote:
On 04/13/2012 06:48 PM, Kenji Kaneshige wrote:
(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
If MMCFG could be treated as an optional configuration space access method,
we can refine the MMCFG code according to Bjorn's suggestion. And as Kenji
has mentioned, there may be some risks ahead. So need more confirmation
from other PCI experts here.
I looked at the thread, but didn't know which suggestion of Bjorn's you were referring to.
But, mmcfg access to PCI config space is need for any cap structure
greater than 256 byte offset. A number of devices have cap structures
in this upper PCI config space, esp. SRIOV devices.
So, if 'optional MMCFG' only means at the beginning of kernel scanning of
PCI (pass-0 scanning), that should be ok, but in-depth, pass-1 scanning
of PCIe devices may require MMCFG for full functional support.
For mainstream systems with support of ACPI and MMCFG, the booting sequences are about:
1) Probe for legacy PCI configuration access mechanism, such as CONF1, CONF2, BIOS
2) Start ACPICA/ACPI subsystem with the legacy PCI configuration access mechanism
3) Enumerate PCI root bridges (PNP0A03/PNP0A08) in ACPI namespace and bind pci_root
driver to them
4) pci_root driver calls into arch code to add MMCFG information for the host bridge
5) pci_root driver calls PCI core to enumerate all PCI devices under the host bridge
The above flow should work for SRIOV case. But still need to check following cases:
1) ACPICA/ACPI subsystem has no dependency on MMCFG
2) Systems implementing SFI instead of ACPI work as expected
3) ACPI has been disabled by user (Bjorn points out we could ignore this case)
Agreed. My least favorite bz: "I set boot param to noacpi and can't scan entire PCI space.... duh!
4) Some host bridges are not reported by ACPI (Bjorn points out we should eventually
get rid of the blind probing logic)
And depend on BIOS-ACPI to be correct all the time? ....hahahahahaha ...
sorry.... you hit my funny bone! ;-)
Is blind probing problematic ?
Seems like a pci-fixup/quirk can be implemented under arch/<>/pci to handle
these cases, and thus, depend on ACPI for host-bridge info... wait! did I just
say depend on ACPI?!?! :)
So we may have a try according to Bjorn's suggestions.
Thanks!
It may be a good idea to ping the ACPI community to check whether ACPICA
has any dependency on the MMCFG mechanism too.
Thanks
Gerry
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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