From: Vidya Sagar <vidyas@nvidia.com>
To: Bjorn Helgaas <helgaas@kernel.org>
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, 1 Apr 2024 13:29:48 +0530 [thread overview]
Message-ID: <0c948351-9715-4c5c-ad0c-3727cd2ba8a8@nvidia.com> (raw)
In-Reply-To: <d93a3f29-b260-4910-aaf5-d734e6242223@nvidia.com>
Hi Bjorn,
Just checking on this thread.
Is there anything else you want me to clarify on?
Thanks,
Vidya Sagar
On 14-03-2024 06:09, Vidya Sagar wrote:
>
>
> On 23-01-2024 04:30, Bjorn Helgaas wrote:
>> External email: Use caution opening links or attachments
>>
>>
>> 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.
> In this case, there won't be any TLP sent downstream. I talked about
> this scenario in the
> second paragraph of point (1) above.
>> 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.
> So far in my testing, clearing it in pci_scan_bridge_extend() covers
> all the cases.
>
>>> 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:[~2024-04-01 7:59 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
2024-03-14 0:39 ` Vidya Sagar
2024-04-01 7:59 ` Vidya Sagar [this message]
2024-04-18 10:52 ` Vidya Sagar
2024-04-23 21:09 ` Bjorn Helgaas
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