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SubjectRe: [PATCH v1 1/1] PCI/AER: Use _OSC negotiation to determine AER ownership
[Austin, help us understand the FIRMWARE_FIRST bit! :)]

On Thu, Apr 30, 2020 at 05:40:22PM -0500, Bjorn Helgaas wrote:
> On Sun, Apr 26, 2020 at 11:30:06AM -0700, sathyanarayanan.kuppuswamy@linux.intel.com wrote:
> > From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> >
> > Currently PCIe AER driver uses HEST FIRMWARE_FIRST bit to
> > determine the PCIe AER Capability ownership between OS and
> > firmware. This support is added based on following spec
> > reference.
> >
> > Per ACPI spec r6.3, table 18-387, 18-388, 18-389, HEST table
> > flags field BIT-0 and BIT-1 can be used to expose the
> > ownership of error source between firmware and OSPM.
> >
> > Bit [0] - FIRMWARE_FIRST: If set, indicates that system
> > firmware will handle errors from this source
> > first.
> > Bit [1] – GLOBAL: If set, indicates that the settings
> > contained in this structure apply globally to all
> > PCI Express Bridges.
> >
> > Although above spec reference states that setting
> > FIRMWARE_FIRST bit means firmware will handle the error source
> > first, it does not explicitly state anything about AER
> > ownership. So using HEST to determine AER ownership is
> > incorrect.
> >
> > Also, as per following specification references, _OSC can be
> > used to negotiate the AER ownership between firmware and OS.
> > Details are,
> >
> > Per ACPI spec r6.3, sec 6.2.11.3, table titled “Interpretation
> > of _OSC Control Field” and as per PCI firmware specification r3.2,
> > sec 4.5.1, table 4-5, OS can set bit 3 of _OSC control field
> > to request control over PCI Express AER. If the OS successfully
> > receives control of this feature, it must handle error reporting
> > through the AER Capability as described in the PCI Express Base
> > Specification.
> >
> > Since above spec references clearly states _OSC can be used to
> > determine AER ownership, don't depend on HEST FIRMWARE_FIRST bit.
>
> I pulled out the _OSC part of this to a separate patch. What's left
> is below, and is essentially equivalent to Alex's patch:
>
> https://lore.kernel.org/r/20190326172343.28946-3-mr.nuke.me@gmail.com/
>
> I like what this does, but what I don't like is the fact that we now
> have this thing called pcie_aer_get_firmware_first() that is not
> connected with the ACPI FIRMWARE_FIRST bit at all.

Austin, if we remove this, we'll have no PCIe-related code that looks
at the HEST FIRMWARE_FIRST bit at all. Presumably it's there for some
reason, but I'm not sure what the reason is.

Alex's mail [1] has a nice table of _OSC AER/HEST FFS bits that looks
useful, but the only actionable thing I can see is that in the (1,1)
case, OSPM should do some initialization with masks/enables.

But I have no clue what that means or how to connect that with the
spec. What are the masks/enables? Is that something connected with
ERST?

[1] https://lore.kernel.org/r/20190326172343.28946-1-mr.nuke.me@gmail.com/

> > diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
> > index f4274d301235..85d73d28ec26 100644
> > --- a/drivers/pci/pcie/aer.c
> > +++ b/drivers/pci/pcie/aer.c
> > @@ -217,133 +217,19 @@ void pcie_ecrc_get_policy(char *str)
> > }
> > #endif /* CONFIG_PCIE_ECRC */
> >
> > -#ifdef CONFIG_ACPI_APEI
> > -static inline int hest_match_pci(struct acpi_hest_aer_common *p,
> > - struct pci_dev *pci)
> > -{
> > - return ACPI_HEST_SEGMENT(p->bus) == pci_domain_nr(pci->bus) &&
> > - ACPI_HEST_BUS(p->bus) == pci->bus->number &&
> > - p->device == PCI_SLOT(pci->devfn) &&
> > - p->function == PCI_FUNC(pci->devfn);
> > -}
> > -
> > -static inline bool hest_match_type(struct acpi_hest_header *hest_hdr,
> > - struct pci_dev *dev)
> > -{
> > - u16 hest_type = hest_hdr->type;
> > - u8 pcie_type = pci_pcie_type(dev);
> > -
> > - if ((hest_type == ACPI_HEST_TYPE_AER_ROOT_PORT &&
> > - pcie_type == PCI_EXP_TYPE_ROOT_PORT) ||
> > - (hest_type == ACPI_HEST_TYPE_AER_ENDPOINT &&
> > - pcie_type == PCI_EXP_TYPE_ENDPOINT) ||
> > - (hest_type == ACPI_HEST_TYPE_AER_BRIDGE &&
> > - (dev->class >> 16) == PCI_BASE_CLASS_BRIDGE))
> > - return true;
> > - return false;
> > -}
> > -
> > -struct aer_hest_parse_info {
> > - struct pci_dev *pci_dev;
> > - int firmware_first;
> > -};
> > -
> > -static int hest_source_is_pcie_aer(struct acpi_hest_header *hest_hdr)
> > -{
> > - if (hest_hdr->type == ACPI_HEST_TYPE_AER_ROOT_PORT ||
> > - hest_hdr->type == ACPI_HEST_TYPE_AER_ENDPOINT ||
> > - hest_hdr->type == ACPI_HEST_TYPE_AER_BRIDGE)
> > - return 1;
> > - return 0;
> > -}
> > -
> > -static int aer_hest_parse(struct acpi_hest_header *hest_hdr, void *data)
> > -{
> > - struct aer_hest_parse_info *info = data;
> > - struct acpi_hest_aer_common *p;
> > - int ff;
> > -
> > - if (!hest_source_is_pcie_aer(hest_hdr))
> > - return 0;
> > -
> > - p = (struct acpi_hest_aer_common *)(hest_hdr + 1);
> > - ff = !!(p->flags & ACPI_HEST_FIRMWARE_FIRST);
> > -
> > - /*
> > - * If no specific device is supplied, determine whether
> > - * FIRMWARE_FIRST is set for *any* PCIe device.
> > - */
> > - if (!info->pci_dev) {
> > - info->firmware_first |= ff;
> > - return 0;
> > - }
> > -
> > - /* Otherwise, check the specific device */
> > - if (p->flags & ACPI_HEST_GLOBAL) {
> > - if (hest_match_type(hest_hdr, info->pci_dev))
> > - info->firmware_first = ff;
> > - } else
> > - if (hest_match_pci(p, info->pci_dev))
> > - info->firmware_first = ff;
> > -
> > - return 0;
> > -}
> > -
> > -static void aer_set_firmware_first(struct pci_dev *pci_dev)
> > -{
> > - int rc;
> > - struct aer_hest_parse_info info = {
> > - .pci_dev = pci_dev,
> > - .firmware_first = 0,
> > - };
> > -
> > - rc = apei_hest_parse(aer_hest_parse, &info);
> > -
> > - if (rc)
> > - pci_dev->__aer_firmware_first = 0;
> > - else
> > - pci_dev->__aer_firmware_first = info.firmware_first;
> > - pci_dev->__aer_firmware_first_valid = 1;
> > -}
> > -
> > int pcie_aer_get_firmware_first(struct pci_dev *dev)
> > {
> > + struct pci_host_bridge *host = pci_find_host_bridge(dev->bus);
> > +
> > if (!pci_is_pcie(dev))
> > return 0;
> >
> > if (pcie_ports_native)
> > return 0;
> >
> > - if (!dev->__aer_firmware_first_valid)
> > - aer_set_firmware_first(dev);
> > - return dev->__aer_firmware_first;
> > + return !host->native_aer;
> > }
>
> > diff --git a/drivers/pci/pcie/portdrv.h b/drivers/pci/pcie/portdrv.h
> > index 64b5e081cdb2..c05b49d740f4 100644
> > --- a/drivers/pci/pcie/portdrv.h
> > +++ b/drivers/pci/pcie/portdrv.h
> > @@ -147,16 +147,7 @@ static inline bool pcie_pme_no_msi(void) { return false; }
> > static inline void pcie_pme_interrupt_enable(struct pci_dev *dev, bool en) {}
> > #endif /* !CONFIG_PCIE_PME */
> >
> > -#ifdef CONFIG_ACPI_APEI
> > int pcie_aer_get_firmware_first(struct pci_dev *pci_dev);
> > -#else
> > -static inline int pcie_aer_get_firmware_first(struct pci_dev *pci_dev)
> > -{
> > - if (pci_dev->__aer_firmware_first_valid)
> > - return pci_dev->__aer_firmware_first;
> > - return 0;
> > -}
> > -#endif
> >
> > struct device *pcie_port_find_device(struct pci_dev *dev, u32 service);
> > #endif /* _PORTDRV_H_ */
> > diff --git a/include/linux/pci.h b/include/linux/pci.h
> > index 83ce1cdf5676..43f265830eca 100644
> > --- a/include/linux/pci.h
> > +++ b/include/linux/pci.h
> > @@ -420,8 +420,6 @@ struct pci_dev {
> > * mappings to make sure they cannot access arbitrary memory.
> > */
> > unsigned int untrusted:1;
> > - unsigned int __aer_firmware_first_valid:1;
> > - unsigned int __aer_firmware_first:1;
> > unsigned int broken_intx_masking:1; /* INTx masking can't be used */
> > unsigned int io_window_1k:1; /* Intel bridge 1K I/O windows */
> > unsigned int irq_managed:1;
> > --
> > 2.17.1
> >

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