Re: [PATCH v2 2/3] PCI/DPC: Remove CONFIG_PCIE_EDR

Bjorn Helgaas
2024-03-01T23:06:06Z

On Sun, Feb 25, 2024 at 12:05:12PM -0800, Kuppuswamy Sathyanarayanan wrote:
> On 2/22/24 2:15 PM, Bjorn Helgaas wrote:
> > From: Bjorn Helgaas <bhelgaas@google.com>
> >
> > Previous Kconfig allowed the possibility of enabling CONFIG_PCIE_DPC
> > without CONFIG_PCIE_EDR. The PCI Firmware Spec, r3.3, sec 4.5.1,
> > table 4-5, says an ACPI OS that requests control of DPC must also
> > advertise support for EDR.
> >
> > Remove CONFIG_PCIE_EDR and enable the EDR code with CONFIG_PCIE_DPC so that
> > enabling DPC also enables EDR for ACPI systems. Since EDR is an ACPI
> > feature, build edr.o only when CONFIG_ACPI is enabled. Stubs cover the
> > case when DPC is enabled without ACPI.
> >
> > Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
> > ---
> > drivers/acpi/pci_root.c | 2 +-
> > drivers/pci/pcie/Kconfig | 14 ++++----------
> > drivers/pci/pcie/Makefile | 5 ++++-
> > drivers/pci/pcie/dpc.c | 10 ----------
> > include/linux/pci-acpi.h | 4 ++--
> > 5 files changed, 11 insertions(+), 24 deletions(-)
> >
> > diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> > index efc292b6214e..bcaf3d3a5e05 100644
> > --- a/drivers/acpi/pci_root.c
> > +++ b/drivers/acpi/pci_root.c
> > @@ -448,7 +448,7 @@ static u32 calculate_support(void)
> > support |= OSC_PCI_ASPM_SUPPORT | OSC_PCI_CLOCK_PM_SUPPORT;
> > if (pci_msi_enabled())
> > support |= OSC_PCI_MSI_SUPPORT;
> > - if (IS_ENABLED(CONFIG_PCIE_EDR))
> > + if (IS_ENABLED(CONFIG_PCIE_DPC)) /* DPC => EDR support */
> > support |= OSC_PCI_EDR_SUPPORT;
>
> Since EDR internally touches AER registers, I still think we should
> make sure OS enables AER support before advertising the EDR support.

I guess you're suggesting that we should make it look like this?

if (host_bridge->native_aer && IS_ENABLED(CONFIG_PCIE_DPC))

That doesn't seem right to me because the implementation note in PCI
Firmware r3.3, sec 4.6.12, shows the EDR flow when firmware maintains
control of AER and DPC, i.e., "host_bridge->native_aer" would be
false.

> > return support;
> > diff --git a/drivers/pci/pcie/Kconfig b/drivers/pci/pcie/Kconfig
> > index 8999fcebde6a..21e98289fbe9 100644
> > --- a/drivers/pci/pcie/Kconfig
> > +++ b/drivers/pci/pcie/Kconfig
> > @@ -137,6 +137,10 @@ config PCIE_DPC
> > have this capability or you do not want to use this feature,
> > it is safe to answer N.
> >
> > + On ACPI systems, this includes Error Disconnect Recover support,
> > + the hybrid model that uses both firmware and OS to implement DPC,
> > + as specified in the PCI Firmware Specification r3.3.
>
> Nit: Include some section reference?

I basically copied this from the PCIE_EDR help and updated the
revision number. But I don't think the firmware spec is a very good
reference because EDR is defined by ACPI. There's very little text in
the ACPI spec about EDR, but the firmware spec does assume you know
what *is* there. And the ACPI spec is available to anybody, unlike
the PCI firmware spec.

+ On ACPI systems, this includes Error Disconnect Recover support,
+ the hybrid model that uses both firmware and OS to implement DPC,
+ as specified in ACPI r6.5, sec 5.6.6.

> > config PCIE_PTM
> > bool "PCI Express Precision Time Measurement support"
> > help
> > @@ -145,13 +149,3 @@ config PCIE_PTM
> >
> > This is only useful if you have devices that support PTM, but it
> > is safe to enable even if you don't.
> > -
> > -config PCIE_EDR
> > - bool "PCI Express Error Disconnect Recover support"
> > - depends on PCIE_DPC && ACPI
> > - help
> > - This option adds Error Disconnect Recover support as specified
> > - in the Downstream Port Containment Related Enhancements ECN to
> > - the PCI Firmware Specification r3.2. Enable this if you want to
> > - support hybrid DPC model which uses both firmware and OS to
> > - implement DPC.