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Date: Thu, 1 Oct 2020 18:14:07 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Sean V Kelley <seanvk.dev@...gontracks.org>
Cc: bhelgaas@...gle.com, Jonathan.Cameron@...wei.com,
rafael.j.wysocki@...el.com, ashok.raj@...el.com,
tony.luck@...el.com, sathyanarayanan.kuppuswamy@...el.com,
qiuxu.zhuo@...el.com, linux-pci@...r.kernel.org,
linux-kernel@...r.kernel.org,
Sean V Kelley <sean.v.kelley@...el.com>
Subject: Re: [PATCH v7 07/13] PCI/AER: Extend AER error handling to RCECs
On Wed, Sep 30, 2020 at 02:58:14PM -0700, Sean V Kelley wrote:
> From: Jonathan Cameron <Jonathan.Cameron@...wei.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_walk_bridge(), similar to pci_walk_bus(),
> 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@...wei.com>
> Signed-off-by: Sean V Kelley <sean.v.kelley@...el.com>
> ---
> drivers/pci/pcie/err.c | 52 +++++++++++++++++++++++++++++++++---------
> 1 file changed, 41 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
> index 9e552330155b..c4ceca42a3bf 100644
> --- a/drivers/pci/pcie/err.c
> +++ b/drivers/pci/pcie/err.c
> @@ -146,44 +146,73 @@ static int report_resume(struct pci_dev *dev, void *data)
> return 0;
> }
>
> +/**
> + * pci_walk_bridge - 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_walk_bridge(struct pci_dev *bridge, int (*cb)(struct pci_dev *, void *),
> + 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_subordinate_devices)(struct pci_dev *pdev))
> {
> 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
> * bridge. If the downstream bridge detected the error, it is
> - * cleared at the end.
> + * cleared at the end. For RCiEPs we should reset just the RCiEP itself.
> */
> type = pci_pcie_type(dev);
> if (type == PCI_EXP_TYPE_ROOT_PORT ||
> - type == PCI_EXP_TYPE_DOWNSTREAM)
> + 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);
>
> - bus = bridge->subordinate;
> pci_dbg(dev, "broadcast error_detected message\n");
> if (state == pci_channel_io_frozen) {
> - pci_walk_bus(bus, report_frozen_detected, &status);
> - status = reset_subordinate_device(dev);
> + pci_walk_bridge(bridge, report_frozen_detected, &status);
Wonder if it would be worth splitting out the pci_walk_bus() to
pci_walk_bridge() change -- initially pci_walk_bridge() would do only
this:
if (bridge->subordinate)
pci_walk_bus(bridge->subordinate, cb, userdata);
so basically just rename it and move the bridge->subordinate
dereference out.
Then the next patch would be a lot smaller and would add the
!bridge->subordinate case (which I think is only for RC_EC & RC_END?)
> + if (type == PCI_EXP_TYPE_RC_END) {
> + pci_warn(dev, "subordinate device reset not possible for RCiEP\n");
> + status = PCI_ERS_RESULT_NONE;
> + goto failed;
> + }
> +
> + status = reset_subordinate_devices(bridge);
I missed the reason for this change:
- status = reset_subordinate_device(dev);
+ status = reset_subordinate_devices(bridge);
> if (status != PCI_ERS_RESULT_RECOVERED) {
> pci_warn(dev, "subordinate device reset failed\n");
> goto failed;
> }
> } else {
> - pci_walk_bus(bus, report_normal_detected, &status);
> + pci_walk_bridge(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_walk_bridge(bridge, report_mmio_enabled, &status);
> }
>
> if (status == PCI_ERS_RESULT_NEED_RESET) {
> @@ -194,17 +223,18 @@ 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_walk_bridge(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);
> + pci_walk_bridge(bridge, report_resume, &status);
>
> if (type == PCI_EXP_TYPE_ROOT_PORT ||
> - type == PCI_EXP_TYPE_DOWNSTREAM) {
> + type == PCI_EXP_TYPE_DOWNSTREAM ||
> + type == PCI_EXP_TYPE_RC_EC) {
> if (pcie_aer_is_native(bridge))
> pcie_clear_device_status(bridge);
> pci_aer_clear_nonfatal_status(bridge);
> --
> 2.28.0
>
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