On Tue, Jun 24, 2025 at 10:16:37AM -0700, Sean Christopherson wrote:
> Query support for Immediate Readiness irrespective of whether or not the
> device supports PM capabilities, as nothing in the PCIe spec suggests that
> Immediate Readiness is in any way dependent on PM functionality.
Huh, I forgot that we had support for Immediate Readiness at all.
I agree, Immediate Readiness has nothing to do with PM except that we
take advantage of it in a PM path, and I think pci_pm_init() was
probably not the best place to put this.
> Opportunistically add a comment to explain why "errors" during PM setup
> are effectively ignored.
>
> Fixes: d6112f8def51 ("PCI: Add support for Immediate Readiness")
> Cc: David Matlack <dmatlack@xxxxxxxxxx>
> Cc: Vipin Sharma <vipinsh@xxxxxxxxxx>
> Cc: Aaron Lewis <aaronlewis@xxxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
>
> RFC as I'm not entirely sure this is useful/correct.
>
> Found by inspection when debugging a VFIO VF passthrough issue that turned out
> to be 907a7a2e5bf4 ("PCI/PM: Set up runtime PM even for devices without PCI PM").
>
> The folks on the Cc list are looking at parallelizing VF assignment to avoid
> serializing the 100ms wait on FLR. I'm hoping we'll get lucky and the VFs in
> question do (or can) support PCI_STATUS_IMM_READY.
>
> drivers/pci/pci.c | 40 +++++++++++++++++++++++++---------------
> 1 file changed, 25 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 9e42090fb108..cd91adbf0269 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -3198,33 +3198,22 @@ void pci_pm_power_up_and_verify_state(struct pci_dev *pci_dev)
> pci_update_current_state(pci_dev, PCI_D0);
> }
>
> -/**
> - * pci_pm_init - Initialize PM functions of given PCI device
> - * @dev: PCI device to handle.
> - */
> -void pci_pm_init(struct pci_dev *dev)
> +static void __pci_pm_init(struct pci_dev *dev)
> {
> int pm;
> - u16 status;
> u16 pmc;
>
> - device_enable_async_suspend(&dev->dev);
> - dev->wakeup_prepared = false;
> -
> - dev->pm_cap = 0;
> - dev->pme_support = 0;
> -
> /* find PCI PM capability in list */
> pm = pci_find_capability(dev, PCI_CAP_ID_PM);
> if (!pm)
> - goto poweron;
> + return;
> /* Check device's ability to generate PME# */
> pci_read_config_word(dev, pm + PCI_PM_PMC, &pmc);
>
> if ((pmc & PCI_PM_CAP_VER_MASK) > 3) {
> pci_err(dev, "unsupported PM cap regs version (%u)\n",
> pmc & PCI_PM_CAP_VER_MASK);
> - goto poweron;
> + return;
> }
>
> dev->pm_cap = pm;
> @@ -3265,11 +3254,32 @@ void pci_pm_init(struct pci_dev *dev)
> /* Disable the PME# generation functionality */
> pci_pme_active(dev, false);
> }
> +}
> +
> +/**
> + * pci_pm_init - Initialize PM functions of given PCI device
> + * @dev: PCI device to handle.
> + */
> +void pci_pm_init(struct pci_dev *dev)
> +{
> + u16 status;
> +
> + device_enable_async_suspend(&dev->dev);
> + dev->wakeup_prepared = false;
> +
> + dev->pm_cap = 0;
> + dev->pme_support = 0;
> +
> + /*
> + * Note, support for the PCI PM spec is optional for legacy PCI devices
> + * and for VFs. Continue on even if no PM capabilities are supported.
> + */
> + __pci_pm_init(dev);
>
> pci_read_config_word(dev, PCI_STATUS, &status);
> if (status & PCI_STATUS_IMM_READY)
> dev->imm_ready = 1;
I would rather just move this PCI_STATUS read to somewhere else. I
don't think there's a great place to put it. We could put it in
set_pcie_port_type(), which is sort of a grab bag of PCIe-related
things.
I don't know if it's necessarily even a PCIe-specific thing, but it
would be unexpected if somebody made a conventional PCI device that
set it, since the bit was reserved (and should be zero) in PCI r3.0
and defined in PCIe r4.0.
Maybe we should put it in pci_setup_device() close to where we call
pci_intx_mask_broken()?
Both PCI_STATUS_IMM_READY and PCI_STATUS_CAP_LIST are read-only, and
we currently read PCI_STATUS for every single pci_find_capability()
call, which is kind of stupid. Maybe someday we can optimize that and
read PCI_STATUS once for both PCI_STATUS_CAP_LIST and
PCI_STATUS_IMM_READY.
> -poweron:
> +
> pci_pm_power_up_and_verify_state(dev);
> pm_runtime_forbid(&dev->dev);
> pm_runtime_set_active(&dev->dev);
>
> base-commit: 86731a2a651e58953fc949573895f2fa6d456841
> --
> 2.50.0.714.g196bf9f422-goog
>
