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SubjectRe: [PATCH 1/5] PCI/DPC: Ignore devices with no AER Capability
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On 11/28/20 3:25 PM, Bjorn Helgaas wrote:
> On Sat, Nov 28, 2020 at 01:56:23PM -0800, Kuppuswamy, Sathyanarayanan wrote:
>> On 11/28/20 1:53 PM, Bjorn Helgaas wrote:
>>> On Sat, Nov 28, 2020 at 01:49:46PM -0800, Kuppuswamy, Sathyanarayanan wrote:
>>>> On 11/28/20 12:24 PM, Bjorn Helgaas wrote:
>>>>> On Wed, Nov 25, 2020 at 06:01:57PM -0800, Kuppuswamy, Sathyanarayanan wrote:
>>>>>> On 11/25/20 5:18 PM, Bjorn Helgaas wrote:
>>>>>>> From: Bjorn Helgaas <bhelgaas@google.com>
>>>>>>>
>>>>>>> Downstream Ports may support DPC regardless of whether they support AER
>>>>>>> (see PCIe r5.0, sec 6.2.10.2). Previously, if the user booted with
>>>>>>> "pcie_ports=dpc-native", it was possible for dpc_probe() to succeed even if
>>>>>>> the device had no AER Capability, but dpc_get_aer_uncorrect_severity()
>>>>>>> depends on the AER Capability.
>>>>>>>
>>>>>>> dpc_probe() previously failed if:
>>>>>>>
>>>>>>> !pcie_aer_is_native(pdev) && !pcie_ports_dpc_native
>>>>>>> !(pcie_aer_is_native() || pcie_ports_dpc_native) # by De Morgan's law
>>>>>>>
>>>>>>> so it succeeded if:
>>>>>>>
>>>>>>> pcie_aer_is_native() || pcie_ports_dpc_native
>>>>>>>
>>>>>>> Fail dpc_probe() if the device has no AER Capability.
>>>>>>>
>>>>>>> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
>>>>>>> Cc: Olof Johansson <olof@lixom.net>
>>>>>>> ---
>>>>>>> drivers/pci/pcie/dpc.c | 3 +++
>>>>>>> 1 file changed, 3 insertions(+)
>>>>>>>
>>>>>>> diff --git a/drivers/pci/pcie/dpc.c b/drivers/pci/pcie/dpc.c
>>>>>>> index e05aba86a317..ed0dbc43d018 100644
>>>>>>> --- a/drivers/pci/pcie/dpc.c
>>>>>>> +++ b/drivers/pci/pcie/dpc.c
>>>>>>> @@ -287,6 +287,9 @@ static int dpc_probe(struct pcie_device *dev)
>>>>>>> int status;
>>>>>>> u16 ctl, cap;
>>>>>>> + if (!pdev->aer_cap)
>>>>>>> + return -ENOTSUPP;
>>>>>> Don't we check aer_cap support in drivers/pci/pcie/portdrv_core.c ?
>>>>>>
>>>>>> We don't enable DPC service, if AER service is not enabled. And AER
>>>>>> service is only enabled if AER capability is supported.
>>>>>>
>>>>>> So dpc_probe() should not happen if AER capability is not supported?
>>>>>
>>>>> I don't think that's always true. If I'm reading this right, we have
>>>>> this:
>>>>>
>>>>> get_port_device_capability(...)
>>>>> {
>>>>> #ifdef CONFIG_PCIEAER
>>>>> if (dev->aer_cap && ...)
>>>>> services |= PCIE_PORT_SERVICE_AER;
>>>>> #endif
>>>>>
>>>>> if (pci_find_ext_capability(dev, PCI_EXT_CAP_ID_DPC) &&
>>>>> pci_aer_available() &&
>>>>> (pcie_ports_dpc_native || (services & PCIE_PORT_SERVICE_AER)))
>>>>> services |= PCIE_PORT_SERVICE_DPC;
>>>>> }
>>>>>
>>>>> and in the case where:
>>>>>
>>>>> - CONFIG_PCIEAER=y
>>>>> - booted with "pcie_ports=dpc-native" (pcie_ports_dpc_native is true)
>>>>> - "dev" has no AER capability
>>>>> - "dev" has DPC capability
>>>>>
>>>>> I think we do enable PCIE_PORT_SERVICE_DPC.
>>>> Got it. But further looking into it, I am wondering whether
>>>> we should keep this dependency? Currently we just use it to
>>>> dump the error information. Do we need to create dependency
>>>> between DPC and AER (which is functionality not dependent) just
>>>> to see more details about the error?
>>>
>>> That's a good question, but I don't really want to get into the actual
>>> operation of the AER and DPC drivers in this series, so maybe
>>> something we should explore later.
>
>> In that case, can you move this check to
>> drivers/pci/pcie/portdrv_core.c? I don't see the point of
>> distributed checks in both get_port_device_capability() and
>> dpc_probe().
>
> I totally agree that these distributed checks are terrible, but my
> long-term hope is to get rid of portdrv and handle these "services"
> more like we handle other capabilities. For example, maybe we can
> squash dpc_probe() into pci_dpc_init(), so I'd actually like to move
> things from get_port_device_capability() into dpc_probe().
Removing the service driver model will be a major overhaul. It would
affect even the error recovery drivers. You can find motivation
for service drivers in Documentation/PCI/pciebus-howto.rst.

But till we fix this part, I recommend grouping all dependency checks
to one place (either dpc_probe() or portdrv service driver).
>

--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer

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