linux-kernel - Re: [PATCH V1] PCI: Clear errors logged in Secondary Status Register

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Date: Fri, 12 Jan 2024 11:06:22 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Vidya Sagar <vidyas@...dia.com>
Cc: bhelgaas@...gle.com, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, treding@...dia.com,
	jonathanh@...dia.com, kthota@...dia.com, mmaddireddy@...dia.com,
	sagar.tv@...il.com
Subject: Re: [PATCH V1] PCI: Clear errors logged in Secondary Status Register

On Thu, Jan 04, 2024 at 07:02:29AM +0530, Vidya Sagar wrote:
> If a downstream port has a PCIe switch connected to it, the enumeration
> process leaves the 'Received Master Abort' bit set in the Secondary
> Status Register of the downstream port because of the Unsupported
> Requests (URs) take place in the downstream hierarchy. Since the
> ownership of Secondary Status Register always lies with the OS including
> systems with Firmware-First approach for error handling[1], clear the
> error status bits in the Secondary Status Register post enumeration.

I would expect these URs to happen when enumerating below *all* PCIe
Root Ports (not just when switches are present), and Master Aborts
should happen in conventional PCI.

Similarly, I don't think Firmware-First is relevant here.  Only the
fact that the OS owns PCI_SEC_STATUS because there's no mechanism to
negotiate for platform ownership of it.

We're in the merge window right now, so we'll start merging v6.9
material after v6.8-rc1 is tagged.

> [1] https://lore.kernel.org/all/1fb9d746-0695-4d19-af98-f442f31cd464@nvidia.com/T/
> 
> Signed-off-by: Vidya Sagar <vidyas@...dia.com>
> ---
>  drivers/pci/probe.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 43159965e09e..edf8202465d8 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1470,6 +1470,9 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
>  	}
>  
>  out:
> +	/* Clear errors in the Secondary Status Register */
> +	pci_write_config_word(dev, PCI_SEC_STATUS, 0xffff);
> +
>  	pci_write_config_word(dev, PCI_BRIDGE_CONTROL, bctl);
>  
>  	pm_runtime_put(&dev->dev);
> -- 
> 2.25.1
>