From: Bjorn Helgaas <helgaas@kernel.org>
To: Vidya Sagar <vidyas@nvidia.com>
Cc: bhelgaas@google.com, linux-pci@vger.kernel.org,
linux-kernel@vger.kernel.org, treding@nvidia.com,
jonathanh@nvidia.com, kthota@nvidia.com, mmaddireddy@nvidia.com,
sagar.tv@gmail.com
Subject: Re: [PATCH V2] PCI: Clear errors logged in Secondary Status Register
Date: Mon, 22 Jan 2024 17:00:26 -0600 [thread overview]
Message-ID: <20240122230026.GA290856@bhelgaas> (raw)
In-Reply-To: <20240116143258.483235-1-vidyas@nvidia.com>
On Tue, Jan 16, 2024 at 08:02:58PM +0530, Vidya Sagar wrote:
> The enumeration process leaves the 'Received Master Abort' bit set in
> the Secondary Status Register of the downstream port in the following
> scenarios.
>
> (1) The device connected to the downstream port has ARI capability
> and that makes the kernel set the 'ARI Forwarding Enable' bit in
> the Device Control 2 Register of the downstream port. This
> effectively makes the downstream port forward the configuration
> requests targeting the devices downstream of it, even though they
> don't exist in reality. It causes the downstream devices return
> completions with UR set in the status in turn causing 'Received
> Master Abort' bit set.
>
> In contrast, if the downstream device doesn't have ARI capability,
> the 'ARI Forwarding Enable' bit in the downstream port is not set
> and any configuration requests targeting the downstream devices
> that don't exist are terminated (section 6.13 of PCI Express Base
> 6.0 spec) in the downstream port itself resulting in no change of
> the 'Received Master Abort' bit.
>
> (2) A PCIe switch is connected to the downstream port and when the
> enumeration flow tries to explore the presence of devices that
> don't really exist downstream of the switch, the downstream
> port receives the completions with UR set causing the 'Received
> Master Abort' bit set.
Are these the only possible ways this error is logged? I expected
them to be logged when we enumerate below a Root Port that has nothing
attached, for example.
Does clearing them in pci_scan_bridge_extend() cover all ways this
error might be logged during enumeration? I can't remember whether
all enumeration goes through this path.
> Clear 'Received Master Abort' bit to keep the bridge device in a clean
> state post enumeration.
>
> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> ---
> V2:
> * Changed commit message based on Bjorn's feedback
>
> drivers/pci/probe.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 795534589b98..640d2871b061 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
>
next prev parent reply other threads:[~2024-01-22 23:00 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-04 1:32 [PATCH V1] PCI: Clear errors logged in Secondary Status Register Vidya Sagar
2024-01-12 13:57 ` Vidya Sagar
2024-01-12 17:06 ` Bjorn Helgaas
2024-01-16 13:54 ` Vidya Sagar
2024-01-16 14:32 ` [PATCH V2] " Vidya Sagar
2024-01-22 23:00 ` Bjorn Helgaas [this message]
2024-03-14 0:39 ` Vidya Sagar
2024-04-01 7:59 ` Vidya Sagar
2024-04-18 10:52 ` Vidya Sagar
2024-04-23 21:09 ` Bjorn Helgaas
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