linux-kernel - Re: [RFC PATCH 5/9] PCI/AER: Apply function level reset to RCiEP on fatal error

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Message-ID: <90E63E9B-DCD3-4325-B1FC-FE5C72BA191B@intel.com>
Date:   Tue, 28 Jul 2020 09:14:11 -0700
From:   "Sean V Kelley" <sean.v.kelley@...el.com>
To:     "Jonathan Cameron" <Jonathan.Cameron@...wei.com>
Cc:     bhelgaas@...gle.com, rjw@...ysocki.net,
        "Zhuo, Qiuxu" <qiuxu.zhuo@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        sathyanarayanan.kuppuswamy@...ux.intel.com,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Raj, Ashok" <ashok.raj@...el.com>
Subject: Re: [RFC PATCH 5/9] PCI/AER: Apply function level reset to RCiEP on
 fatal error

On 28 Jul 2020, at 6:27, Zhuo, Qiuxu wrote:

>> From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
>> Sent: Monday, July 27, 2020 7:17 PM
>> To: Kelley, Sean V <sean.v.kelley@...el.com>
>> Cc: bhelgaas@...gle.com; rjw@...ysocki.net; ashok.raj@...nel.org; 
>> Luck,
>> Tony <tony.luck@...el.com>;
>> sathyanarayanan.kuppuswamy@...ux.intel.com; 
>> linux-pci@...r.kernel.org;
>> linux-kernel@...r.kernel.org; Zhuo, Qiuxu <qiuxu.zhuo@...el.com>
>> Subject: Re: [RFC PATCH 5/9] PCI/AER: Apply function level reset to 
>> RCiEP
>> on fatal error
>>
>> On Fri, 24 Jul 2020 10:22:19 -0700
>> Sean V Kelley <sean.v.kelley@...el.com> wrote:
>>
>>> From: Qiuxu Zhuo <qiuxu.zhuo@...el.com>
>>>
>>> Attempt to do function level reset for an RCiEP associated with an
>>> RCEC device on fatal error.
>>
>> I'd like to understand more on your reasoning for flr here.
>> Is it simply that it is all we can do, or is there some basis in a 
>> spec
>> somewhere?
>>
>
> Yes. Though there isn't the link reset for the RCiEP here, I think we 
> should still be able to reset the RCiEP via FLR on fatal error, if the 
> RCiEP supports FLR.
>
> -Qiuxu
>

Also see PCIe 5.0-1, Sec. 6.6.2 Function Level Reset (FLR)

Implementation of FLR is optional (not required), but is strongly 
recommended. For an example use case consider CXL. Function 0 DVSEC 
instances control for the CXL functionality of the entire CXL device. 
FLR may succeed in recovering from CXL.io domain errors.

Thanks,

Sean

>>>
>>> Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@...el.com>
>>> ---
>>>  drivers/pci/pcie/err.c | 31 ++++++++++++++++++++++---------
>>>  1 file changed, 22 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c index
>>> 044df004f20b..9b3ec94bdf1d 100644
>>> --- a/drivers/pci/pcie/err.c
>>> +++ b/drivers/pci/pcie/err.c
>>> @@ -170,6 +170,17 @@ static void pci_walk_dev_affected(struct
>> pci_dev *dev, int (*cb)(struct pci_dev
>>>  }
>>>  }
>>>
>>> +static enum pci_channel_state flr_on_rciep(struct pci_dev *dev) {
>>> +if (!pcie_has_flr(dev))
>>> +return PCI_ERS_RESULT_NONE;
>>> +
>>> +if (pcie_flr(dev))
>>> +return PCI_ERS_RESULT_DISCONNECT;
>>> +
>>> +return PCI_ERS_RESULT_RECOVERED;
>>> +}
>>> +
>>>  pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>>>  enum pci_channel_state state,
>>>  pci_ers_result_t (*reset_link)(struct pci_dev *pdev))
>> @@ -191,15
>>> +202,17 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>>>  if (state == pci_channel_io_frozen) {
>>>  pci_walk_dev_affected(dev, report_frozen_detected,
>> &status);
>>>  if (pci_pcie_type(dev) == PCI_EXP_TYPE_RC_END) {
>>> -pci_warn(dev, "link reset not possible for RCiEP\n");
>>> -status = PCI_ERS_RESULT_NONE;
>>> -goto failed;
>>> -}
>>> -
>>> -status = reset_link(dev);
>>> -if (status != PCI_ERS_RESULT_RECOVERED) {
>>> -pci_warn(dev, "link reset failed\n");
>>> -goto failed;
>>> +status = flr_on_rciep(dev);
>>> +if (status != PCI_ERS_RESULT_RECOVERED) {
>>> +pci_warn(dev, "function level reset failed\n");
>>> +goto failed;
>>> +}
>>> +} else {
>>> +status = reset_link(dev);
>>> +if (status != PCI_ERS_RESULT_RECOVERED) {
>>> +pci_warn(dev, "link reset failed\n");
>>> +goto failed;
>>> +}
>>>  }
>>>  } else {
>>>  pci_walk_dev_affected(dev, report_normal_detected,
>> &status);
>>