Re: [PATCH] PCI/AER: Enable SERR# forwarding in non ACPI flow

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On 2018-07-13 19:25, Bharat Kumar Gogada wrote:
> Currently PCI_BRIDGE_CTL_SERR is being enabled only in ACPI flow.
> This bit is required for forwarding errors reported by EP devices to
> upstream device.
> This patch enables SERR# for Type-1 PCI device.
>
> Signed-off-by: Bharat Kumar Gogada <bharat.kumar.gogada@xxxxxxxxxx>
> ---
>  drivers/pci/pcie/aer.c |   23 +++++++++++++++++++++++
>  1 files changed, 23 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c index
> a2e8838..943e084 100644
> --- a/drivers/pci/pcie/aer.c
> +++ b/drivers/pci/pcie/aer.c
> @@ -343,6 +343,19 @@ int pci_enable_pcie_error_reporting(struct
> pci_dev
> *dev)
>  	if (!dev->aer_cap)
>  		return -EIO;
>
> +	if (!IS_ENABLED(CONFIG_ACPI) &&
> +	    dev->hdr_type == PCI_HEADER_TYPE_BRIDGE) {
> +		u16 control;
> +
> +		/*
> +		 * A Type-1 PCI bridge will not forward ERR_ messages
coming
> +		 * from an endpoint if SERR# forwarding is not enabled.
> +		 */
> +		pci_read_config_word(dev, PCI_BRIDGE_CONTROL,
&control);
> +		control |= PCI_BRIDGE_CTL_SERR;
> +		pci_write_config_word(dev, PCI_BRIDGE_CONTROL, control);
> +	}
> +
>  	return pcie_capability_set_word(dev, PCI_EXP_DEVCTL,
> PCI_EXP_AER_FLAGS);  }
> EXPORT_SYMBOL_GPL(pci_enable_pcie_error_reporting);
> @@ -352,6 +365,16 @@ int pci_disable_pcie_error_reporting(struct
> pci_dev *dev)
>  	if (pcie_aer_get_firmware_first(dev))
>  		return -EIO;
>
> +	if (!IS_ENABLED(CONFIG_ACPI) &&
> +	    dev->hdr_type == PCI_HEADER_TYPE_BRIDGE) {
> +		u16 control;
> +
> +		/* Clear SERR Forwarding */
> +		pci_read_config_word(dev, PCI_BRIDGE_CONTROL,
&control);
> +		control &= ~PCI_BRIDGE_CTL_SERR;
> +		pci_write_config_word(dev, PCI_BRIDGE_CONTROL, control);
> +	}
> +
>  	return pcie_capability_clear_word(dev, PCI_EXP_DEVCTL,
>  					  PCI_EXP_AER_FLAGS);
>  }


Should this configuration no be set by Firmware ? why should Linux dictate it
?
Hi Oza, Can you please let us know why this should be set by firmware ?
Spec clearly states ERR_CORR,ERR_FATAL/NON FATAL will be forwarded
only if this bit is set.
If linux AER service is being enabled without checking/setting this
bit, then AER service will
not do anything even ERR_* is seen on link.

Regards,
Bharat


The ERR_* to be forwarded or not to be forwarded could be decision of the platform. hence I think it is best left to firmware to decide if it want to enable this for particular platform.

although,
There are 2 cases
Hotplug capable bridge and otherwise.

1) If Firmware sets them, I do not think during enumeraion linux will loose those settings.

2) I do not see any integration of hotplug with AER currently, so if the PCIe switch is plugged into Hotplug
capable RP, I am not very sure if this functions get called.

Keith, Lukas and Bjorn any comments ?

Regards,
Oza.














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