linux-kernel - Re: [PATCH v2] PCI/AER: Enable SERR# forwarding in non ACPI flow

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Date:   Thu, 09 Aug 2018 20:41:27 +0530
From:   poza@...eaurora.org
To:     Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        bhelgaas@...gle.com, rgummal@...inx.com,
        linux-pci-owner@...r.kernel.org
Subject: Re: [PATCH v2] PCI/AER: Enable SERR# forwarding in non ACPI flow

On 2018-08-09 20:27, Bharat Kumar Gogada wrote:
> As per Figure 6-3 in PCIe r4.0, sec 6.2.6, ERR_ messages
> will be forwarded from the secondary interface to the primary 
> interface,
> if the SERR# Enable bit in the Bridge Control register is set.
> Currently PCI_BRIDGE_CTL_SERR is being enabled only in
> ACPI flow.
> This patch enables PCI_BRIDGE_CTL_SERR for Type-1 PCI device.
> 
> Signed-off-by: Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>
> ---
>  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..4fb0d24 100644
> --- a/drivers/pci/pcie/aer.c
> +++ b/drivers/pci/pcie/aer.c
> @@ -343,6 +343,20 @@ int pci_enable_pcie_error_reporting(struct pci_dev 
> *dev)
>  	if (!dev->aer_cap)
>  		return -EIO;
> 
> +	if (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);
> +		if (!(control & PCI_BRIDGE_CTL_SERR)) {
> +			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 +366,15 @@ int pci_disable_pcie_error_reporting(struct 
> pci_dev *dev)
>  	if (pcie_aer_get_firmware_first(dev))
>  		return -EIO;
> 
> +	if (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);
>  }


Hi Bjorn,

I made some comments on patchv1., same I am putting it across here.

what about hot-plug case ?
should not aer_init() call pci_enable_pcie_error_reporting() for all
the downstream pci_dev ?
and remove all the calls from drivers..
aer_init will be called for each device (pci_dev) while pciehp does 
re-enumeration.
so probable we might want to call pci_enable_pcie_error_reporting()
but that dictates the design where AER framework is taking decision to 
enable error reporting on behalf of drivers as well.
but thats fine I think, if drivers do not want to participate then they 
have to call  pci_disable_pcie_error_reporting explicitly.
does this make sense ?