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SubjectRe: [PATCH v7 07/13] PCI/AER: Extend AER error handling to RCECs
Date
On 1 Oct 2020, at 16:14, Bjorn Helgaas wrote:

> On Wed, Sep 30, 2020 at 02:58:14PM -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_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@huawei.com>
>> Signed-off-by: Sean V Kelley <sean.v.kelley@intel.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.

Sure, that’s fine. It was actually something that crossed my mind when
I was doing this prior splitting out because I realized I still needed
to dereference the bus and was disappointed to keep it here.


>
> 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?)

Correct the check on bridge && bridge->subordinate comes in with the
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);

This should have happened in the ‘bridge’ renaming patch. This was
going to be either a reset of dev or dev->bus->self depending on the
type via the assignment of dev = prior to renaming in (5/13). I should
move this change back to the bridge renaming patch.

Thanks,

Sean

>
>> 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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