On Wed, Nov 15, 2017 at 10:26:48AM +0530, Oza Pawandeep wrote:
> PCI Express Base Specification, Rev. 4.0 Version 0.9
> 6.2.10: Downstream Port Containment (DPC)
>
> DPC is an optional normative feature of a Downstream Port. DPC halts PCI
> Express traffic below a Downstream Port after an unmasked uncorrectable
> error is detected at or below the Port, avoiding the potential spread of
> any data corruption, and permitting error recovery if supported by
> software
>
> Triggering DPC disables its Link by directing the LTSSM to the Disabled
> state. Once the LTSSM reaches the Disabled state, it remains in that
> state until the DPC Trigger Status bit is Cleared
>
> So when DPC service is active and registered to port driver, AER should
> not attempt to recover, since DPC will be removing downstream devices,
> and do the recovery.
>
> Signed-off-by: Oza Pawandeep <poza@xxxxxxxxxxxxxx>
>
> diff --git a/drivers/pci/pcie/aer/aerdrv_core.c b/drivers/pci/pcie/aer/aerdrv_core.c
> index 7448052..a9108ea 100644
> --- a/drivers/pci/pcie/aer/aerdrv_core.c
> +++ b/drivers/pci/pcie/aer/aerdrv_core.c
> @@ -482,6 +482,27 @@ static pci_ers_result_t reset_link(struct pci_dev *dev)
> }
>
> /**
> + * pcie_port_query_uptream_service - query upstream service
> + * @dev: pointer to a pci_dev data structure of agent detecting an error
> + * @service: service to be queried
> + *
> + * Invoked to know the status of the service for pci device.
> + */
> +static bool pcie_port_query_uptream_service(struct pci_dev *dev, u32 service)
> +{
> + struct pci_dev *upstream_dev = dev;
> +
> + do {
> + if (pcie_port_query_service(upstream_dev, service))
> + return true;
> + upstream_dev = pcie_port_upstream_bridge(upstream_dev);
> + } while (upstream_dev);
> +
> + return false;
> +}
> +
> +
> +/**
> * do_recovery - handle nonfatal/fatal error recovery process
> * @dev: pointer to a pci_dev data structure of agent detecting an error
> * @severity: error severity type
> @@ -495,6 +516,18 @@ static void do_recovery(struct pci_dev *dev, int severity)
> pci_ers_result_t status, result = PCI_ERS_RESULT_RECOVERED;
> enum pci_channel_state state;
>
> + /*
> + * If DPC is enabled, there is no need to attempt recovery.
> + * Since DPC disables its Link by directing the LTSSM to
> + * the Disabled state.
> + * DPC driver will take care of the recovery, there is no need
> + * for AER driver to race.
> + */
> + if (pcie_port_query_uptream_service(dev, PCIE_PORT_SERVICE_DPC)) {
> + dev_info(&dev->dev, "AER: Device recovery to be done by DPC\n");
> + return;
> + }
What happens without this test?
Does AER read registers from the now-disabled device and get ~0 data?
Or is AER reading registers from the port upstream from the disabled
device and trying to reset the device?
It looks like get_device_error_info() reads registers and doesn't
check to see whether it gets ~0 back. I'm wondering if we *should* be
checking there and whether doing that would help mitigate the issue
here.
I don't really like the pcie_port_query_uptream_service() approach
(BTW, the name is misspelled) because it feels a little ad hoc and it
makes assumptions here in the AER code about what the DPC code is
doing, e.g., how it has configured PCI_EXP_DPC_CTL.
> if (severity == AER_FATAL)
> state = pci_channel_io_frozen;
> else
> --
> Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.,
> a Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
>
>
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