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SubjectRe: [PATCH v6 04/10] PCI/AER: Extend AER error handling to RCECs
[+cc Sinan, who's been reviewing changes in this area (thanks, Sinan!)]

On Tue, Sep 22, 2020 at 02:38:53PM -0700, Sean V Kelley wrote:
> From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>
> Currently the kernel does not handle AER errors for Root Complex
> integrated End Points (RCiEPs)[0]. These devices sit on a root bus within
> the Root Complex (RC). AER handling is performed by a Root Complex Event
> Collector (RCEC) [1] which is a effectively a type of RCiEP on the same
> root bus.
>
> For an RCEC (technically not a Bridge), error messages "received" from
> associated RCiEPs must be enabled for "transmission" in order to cause a
> System Error via the Root Control register or (when the Advanced Error
> Reporting Capability is present) reporting via the Root Error Command
> register and logging in the Root Error Status register and Error Source
> Identification register.
>
> In addition to the defined OS level handling of the reset flow for the
> associated RCiEPs of an RCEC, it is possible to also have non-native
> handling. In that case there is no need to take any actions on the RCEC
> because the firmware is responsible for them. This is true where APEI [2]
> is used to report the AER errors via a GHES[v2] HEST entry [3] and
> relevant AER CPER record [4] and non-native handling is in use.
>
> We effectively end up with two different types of discovery for
> purposes of handling AER errors:
>
> 1) Normal bus walk - we pass the downstream port above a bus to which
> the device is attached and it walks everything below that point.
>
> 2) An RCiEP with no visible association with an RCEC as there is no need
> to walk devices. In that case, the flow is to just call the callbacks for
> the actual device, which in turn references its associated RCEC.
>
> A new walk function pci_bridge_walk(), similar to pci_bus_walk(),
> is provided that takes a pci_dev instead of a bus. If that bridge
> corresponds to a downstream port it will walk the subordinate bus of
> that bridge. If the device does not then it will call the function on
> that device alone.
>
> [0] ACPI PCI Express Base Specification 5.0-1 1.3.2.3 Root Complex
> Integrated Endpoint Rules.
> [1] ACPI PCI Express Base Specification 5.0-1 6.2 Error Signalling and
> Logging
> [2] ACPI Specification 6.3 Chapter 18 ACPI Platform Error Interface (APEI)
> [3] ACPI Specification 6.3 18.2.3.7 Generic Hardware Error Source
> [4] UEFI Specification 2.8, N.2.7 PCI Express Error Section
>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Signed-off-by: Sean V Kelley <sean.v.kelley@intel.com>

I like this patch. I think there are a few things that could be
peeled off as "no functional change" preliminary patches to make the
important changes more obvious in the "money patch".

> ---
> drivers/pci/pci.h | 2 +-
> drivers/pci/pcie/err.c | 77 +++++++++++++++++++++++++++++++-----------
> 2 files changed, 59 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 83670a6425d8..7b547fc3679a 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -575,7 +575,7 @@ static inline int pci_dev_specific_disable_acs_redir(struct pci_dev *dev)
> /* PCI error reporting and recovery */
> pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
> pci_channel_state_t state,
> - pci_ers_result_t (*reset_link)(struct pci_dev *pdev));
> + pci_ers_result_t (*reset_subordinate_devices)(struct pci_dev *pdev));
>
> bool pcie_wait_for_link(struct pci_dev *pdev, bool active);
> #ifdef CONFIG_PCIEASPM
> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
> index c543f419d8f9..e575fa6cee63 100644
> --- a/drivers/pci/pcie/err.c
> +++ b/drivers/pci/pcie/err.c
> @@ -146,38 +146,73 @@ static int report_resume(struct pci_dev *dev, void *data)
> return 0;
> }
>
> +/**
> + * pci_bridge_walk - walk bridges potentially AER affected
> + * @bridge bridge which may be an RCEC with associated RCiEPs,
> + * an RCiEP associated with an RCEC, or a Port.
> + * @cb callback to be called for each device found
> + * @userdata arbitrary pointer to be passed to callback.
> + *
> + * If the device provided is a bridge, walk the subordinate bus,
> + * including any bridged devices on buses under this bus.
> + * Call the provided callback on each device found.
> + *
> + * If the device provided has no subordinate bus, call the provided
> + * callback on the device itself.
> + */
> +static void pci_bridge_walk(struct pci_dev *bridge, int (*cb)(struct pci_dev *, void *),

Maybe call this pci_walk_bridge() so it's the same order as the
existing pci_walk_bus(), unless there's some reason to be different.

> + void *userdata)
> +{
> + if (bridge->subordinate)
> + pci_walk_bus(bridge->subordinate, cb, userdata);
> + else
> + cb(bridge, userdata);
> +}
> +
> pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
> pci_channel_state_t state,
> - pci_ers_result_t (*reset_link)(struct pci_dev *pdev))
> + pci_ers_result_t (*reset_subordinate_devices)(struct pci_dev *pdev))

The rename to "reset_subordinate_devices" seems separable, since it
doesn't change the interface.

> {
> pci_ers_result_t status = PCI_ERS_RESULT_CAN_RECOVER;
> - struct pci_bus *bus;
> + struct pci_dev *bridge;
> + int type;
>
> /*
> - * Error recovery runs on all subordinates of the first downstream port.
> - * If the downstream port detected the error, it is cleared at the end.
> + * Error recovery runs on all subordinates of the first downstream
> + * bridge. If the downstream bridge detected the error, it is
> + * cleared at the end. For RCiEPs we should reset just the RCiEP itself.
> */
> - if (!(pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT ||
> - pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM))
> - dev = dev->bus->self;
> - bus = dev->subordinate;
> + type = pci_pcie_type(dev);
> + if (type == PCI_EXP_TYPE_ROOT_PORT ||
> + type == PCI_EXP_TYPE_DOWNSTREAM ||
> + type == PCI_EXP_TYPE_RC_EC ||
> + type == PCI_EXP_TYPE_RC_END)
> + bridge = dev;
> + else
> + bridge = pci_upstream_bridge(dev);

This makes it much easier to read, thank you. I think the addition of
"type", rename of "dev" to "bridge", the inversion of the condition
(major improvement, thanks again), and use of pci_upstream_bridge()
instead of dev->bus->self might also be separable?

Of course, you'd have to add the RC_EC and RC_END cases later, in the
money patch, but that's a good thing because it won't get lost in all
the other things being changed.

> pci_dbg(dev, "broadcast error_detected message\n");
> if (state == pci_channel_io_frozen) {
> - pci_walk_bus(bus, report_frozen_detected, &status);
> - status = reset_link(dev);
> + pci_bridge_walk(bridge, report_frozen_detected, &status);
> + if (type == PCI_EXP_TYPE_RC_END) {
> + pci_warn(dev, "link reset not possible for RCiEP\n");
> + status = PCI_ERS_RESULT_NONE;
> + goto failed;
> + }
> +
> + status = reset_subordinate_devices(bridge);
> if (status != PCI_ERS_RESULT_RECOVERED) {
> - pci_warn(dev, "link reset failed\n");
> + pci_warn(dev, "subordinate device reset failed\n");
> goto failed;
> }
> } else {
> - pci_walk_bus(bus, report_normal_detected, &status);
> + pci_bridge_walk(bridge, report_normal_detected, &status);
> }
>
> if (status == PCI_ERS_RESULT_CAN_RECOVER) {
> status = PCI_ERS_RESULT_RECOVERED;
> pci_dbg(dev, "broadcast mmio_enabled message\n");
> - pci_walk_bus(bus, report_mmio_enabled, &status);
> + pci_bridge_walk(bridge, report_mmio_enabled, &status);
> }
>
> if (status == PCI_ERS_RESULT_NEED_RESET) {
> @@ -188,18 +223,22 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
> */
> status = PCI_ERS_RESULT_RECOVERED;
> pci_dbg(dev, "broadcast slot_reset message\n");
> - pci_walk_bus(bus, report_slot_reset, &status);
> + pci_bridge_walk(bridge, report_slot_reset, &status);
> }
>
> if (status != PCI_ERS_RESULT_RECOVERED)
> goto failed;
>
> pci_dbg(dev, "broadcast resume message\n");
> - pci_walk_bus(bus, report_resume, &status);
> -
> - if (pcie_aer_is_native(dev))
> - pcie_clear_device_status(dev);
> - pci_aer_clear_nonfatal_status(dev);
> + pci_bridge_walk(bridge, report_resume, &status);
> +
> + if (type == PCI_EXP_TYPE_ROOT_PORT ||
> + type == PCI_EXP_TYPE_DOWNSTREAM ||
> + type == PCI_EXP_TYPE_RC_EC) {

Addition of this check also seems worthy of a separate patch (for just
root ports and downstream ports first, then RC_EC being added later).
That would make a convenient place to explain why we need the change.
I think it's *correct*; it just gets lost in the noise and not even
mentioned when it's done as part of one big patch.

> + if (pcie_aer_is_native(bridge))
> + pcie_clear_device_status(bridge);
> + pci_aer_clear_nonfatal_status(bridge);
> + }
> pci_info(dev, "device recovery successful\n");
> return status;
>
> --
> 2.28.0
>

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