On 04/23/2012 01:41 PM, Bjorn Helgaas wrote:
On Mon, Apr 16, 2012 at 11:54 AM, Don Dutile<ddutile@xxxxxxxxxx> wrote:
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?!?! :)
Hope your funny bone has stopped tingling by now :)
Not when ACPI's always there to bang it again! ;-)
When we probe blindly, we don't know what resources are available on
the bus (except for AMD systems). Therefore, we can't do reliable
assignment, and we have to rely on whatever the BIOS did.
Blind probing finds devices not exposed by the BIOS. This might be a
BIOS bug, or it might be a conscious decision to hide the devices from
the OS. Some OEMs hide devices to reduce the likelihood of users
messing things up with setpci.
It would be interesting and relatively easy to figure out whether
Windows ever discovers a device behind an unreported host bridge. My
guess is "no," but I haven't had time to verify this.
Bjorn
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Well, call me crazy(again!), but why put a host-bridge device on a system
and then (try to) hide it with software(BIOS/ACPI) ?
Sounds like a recipe for disaster if the OS tries to
reconfigure address space or bus-number space.....
then again, mmconfig is tied to acpi (for x86) and maybe more ACPI
magic can restrict cfg space regions to alleviate this problem/issue/condition/practice.
Hiding a PCI device is as simple as not loading its driver... :)
Have to run.... /me has to tell associate to get a new BIOS update
b/c when they enable the BIOS option for IOMMU, the
ACPI DMAR tables are borked.... glad paranoid checks
were added to the Linux IOMMU setup code for the ACPI-DMAR tables!
... of course, assuming such an update exists ....
another borked ACPI table strikes again! :) :) :) ... that's my funny
bone being hit again!
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