Re: [Resend with Ack][PATCH v1] PCI: allow acpiphp to handle PCIeports without native PCIe hotplug capability

From: Bjorn Helgaas
Date: Tue Jul 03 2012 - 11:59:41 EST

On Mon, Jul 2, 2012 at 10:16 PM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote:
> On Mon, Jun 4, 2012 at 1:44 AM, Jiang Liu <jiang.liu@xxxxxxxxxx> wrote:
>> Commit 0d52f54e2ef64c189dedc332e680b2eb4a34590a (PCI / ACPI: Make acpiphp
>> ignore root bridges using PCIe native hotplug) added code that made the
>> acpiphp driver completely ignore PCIe root complexes for which the kernel
>> had been granted control of the native PCIe hotplug feature by the BIOS
>> through _OSC. Later commit 619a5182d1f38a3d629ee48e04fa182ef9170052
>> "PCI hotplug: Always allow acpiphp to handle non-PCIe bridges" relaxed
>> the constraints to allow acpiphp driver handle non-PCIe bridges under
>> such a complex. The constraint needs to be relaxed further to allow
>> acpiphp driver to hanlde PCIe ports without native PCIe hotplug capability.
>> Some MR-IOV switch chipsets, such PLX8696, support multiple virtual PCIe
>> switches and may migrate downstream ports among virtual switches.
>> To migrate a downstream port from the source virtual switch to the target,
>> the port needs to be hot-removed from the source and hot-added into the
>> target. pciehp driver can't be used here because there's no slots within
>> the virtual PCIe switch. So acpiphp driver is used to support downstream
>> port migration. A typical configuration is as below:
>> [Root w/o native PCIe HP]
>> [Upstream port of vswitch w/o native PCIe HP]
>> [Downstream port of vswitch w/ native PCIe HP]
>> [PCIe enpoint]
>> Here acpiphp driver will be used to handle root ports and upstream port
>> in the virtual switch, and pciehp driver will be used to handle downstream
>> ports in the virtual switch.
>> Acked-by: Rafael J. Wysocki <rjw@xxxxxxx>
>> Signed-off-by: Jiang Liu <liuj97@xxxxxxxxx>
>> ---
>> drivers/pci/hotplug/acpiphp_glue.c | 49 ++++++++++++++++++++++++++++-------
>> 1 files changed, 39 insertions(+), 10 deletions(-)
>> diff --git a/drivers/pci/hotplug/acpiphp_glue.c b/drivers/pci/hotplug/acpiphp_glue.c
>> index 806c44f..4889448 100644
>> --- a/drivers/pci/hotplug/acpiphp_glue.c
>> +++ b/drivers/pci/hotplug/acpiphp_glue.c
>> @@ -115,6 +115,43 @@ static const struct acpi_dock_ops acpiphp_dock_ops = {
>> .handler = handle_hotplug_event_func,
>> };
>> +/* Check whether device is managed by native PCIe hotplug driver */
>> +static bool device_is_managed_by_native_pciehp(struct pci_dev *pdev)
>> +{
>> + int pos;
>> + u16 reg16;
>> + u32 reg32;
>> + acpi_handle tmp;
>> + struct acpi_pci_root *root;
>> +
>> + if (!pci_is_pcie(pdev))
>> + return false;
>> +
>> + /* Check whether PCIe port supports native PCIe hotplug */
>> + pos = pci_pcie_cap(pdev);
> Add "if (!pos) return false;" here and you can drop the "if
> (!pci_is_pcie())" test above.
>> + pci_read_config_word(pdev, pos + PCI_EXP_FLAGS, &reg16);
>> + if (!(reg16 & PCI_EXP_FLAGS_SLOT))
> I think this is unsafe. Per the PCIe v3.0 spec, sec 7.8.2 on p648,
> the "Slot Implemented" bit is undefined except for Downstream Ports,
> so we're using an undefined bit to decide whether to read
> If the device has a v1 PCIe Capability, it is not required to even
> implement PCI_EXP_SLTCAP, so we could be reading garbage out of an
> unrelated capability. This is in sec 7.8, p363, of the v1.1 PCIe
> spec. I think v3.0 of the spec is dangerously incomplete because it
> doesn't include enough information to handle the v1 PCIe Capability
> correctly.
> There's a fair amount of work to fix this. I started doing it, but
> decided I didn't have time to complete it. Here's what I think we
> (and by "we," I'm afraid I mean "you" :)) should do:
> - Add a "u16 pcie_flags" field in struct pci_dev and save the "PCI
> Express Capabilities Register" there in set_pcie_port_type(). All
> fields in that register are read-only, so it should be safe to cache
> it.
> - Remove pcie_type from struct pci_dev and replace it with a
> pcie_type() inline that extracts it from pcie_flags.
> - Rework the pcie_cap_has_*() macros in drivers/pci/pci.c to take a
> struct pci_dev * and use pcie_flags instead of type and flags. This
> will remove the need for callers to read the flags themselves.
> - Move the pcie_cap_has_*() macros to include/linux/pci_reg.h so
> they can be shared.
> - Audit all uses of the Link registers (PCI_EXP_LNKCAP,
> PCI_EXP_RTCTL, PCI_EXP_RTSTA) to make sure the register exists, either
> by using pcie_cap_has_*() or some other knowledge of the device.

Thinking about this some more, this still leaves the callers
responsible for using pcie_cap_has_*(), which feels pretty

I wonder if it'd be worth adding interfaces like:

pcie_cap_read_word(const struct pci_dev *, int where, u16 *val);
pcie_cap_read_dword(const struct pci_dev *, int where, u32 *val);
pcie_cap_write_word(const struct pci_dev *, int where, u16 val);
pcie_cap_write_dword(const struct pci_dev *, int where, u32 val);

We might be able to encapsulate the v1/v2 differences inside these, e.g.,

int pcie_cap_read_word(const struct pci_dev *dev, int where, u16 *val)
int pos;

pos = pci_pcie_cap(dev);
if (!pos)
return -EINVAL;

switch (where) {
return pci_read_config_word(dev, pos + where, val);
if (pcie_cap_has_lnkctl(dev))
return pci_read_config_word(dev, pos + where, val);
else {
*val = 0;
return 0;
if (pcie_cap_has_sltctl(dev))
return pci_read_config_word(dev, pos + where, val);
else {
*val = 0;
if (where == PCI_EXP_SLTSTA && dev->pcie_type ==
return 0;
return -EINVAL;

Any thoughts?
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