Date:   Mon, 19 Oct 2020 13:50:17 -0700
From:   "Sean V Kelley" <sean.v.kelley@...el.com>
To:     "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     "Ethan Zhao" <xerces.zhao@...il.com>,
        "Bjorn Helgaas" <helgaas@...nel.org>,
        "Sean V Kelley" <seanvk.dev@...gontracks.org>,
        Jonathan.Cameron@...wei.com, "Bjorn Helgaas" <bhelgaas@...gle.com>,
        rafael.j.wysocki@...el.com, "Ashok Raj" <ashok.raj@...el.com>,
        tony.luck@...el.com, qiuxu.zhuo@...el.com,
        linux-pci <linux-pci@...r.kernel.org>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        "Christoph Hellwig" <hch@....de>, "Sinan Kaya" <okaya@...nel.org>,
        "Keith Busch" <kbusch@...nel.org>
Subject: Re: [PATCH v9 12/15] PCI/RCEC: Add RCiEP's linked RCEC to AER/ERR

On 19 Oct 2020, at 11:59, Kuppuswamy, Sathyanarayanan wrote:

> On 10/19/20 11:31 AM, Sean V Kelley wrote:
>> On 19 Oct 2020, at 3:49, Ethan Zhao wrote:
>>
>>> On Sat, Oct 17, 2020 at 6:29 AM Bjorn Helgaas <helgaas@...nel.org> 
>>> wrote:
>>>>
>>>> [+cc Christoph, Ethan, Sinan, Keith; sorry should have cc'd you to
>>>> begin with since you're looking at this code too. Particularly
>>>> interested in your thoughts about whether we should be touching
>>>> PCI_ERR_ROOT_COMMAND and PCI_ERR_ROOT_STATUS when we don't own 
>>>> AER.]
>>>
>>> aer_root_reset() function has a prefix  'aer_', looks like it's a
>>> function of aer driver, will
>>> only be called by aer driver at runtime. if so it's up to the
>>> owner/aer to know if OSPM is
>>> granted to init. while actually some of the functions and runtime 
>>> service of
>>> aer driver is also shared by GHES driver (running time) and DPC 
>>> driver
>>> (compiling time ?)
>>> etc. then it is confused now.
>>>
>>> Shall we move some of the shared functions and running time service 
>>> to
>>> pci/err.c ?
>>> if so , just like pcie_do_recovery(), it's share by firmware_first  
>>> mode GHES
>>> ghes_probe()
>>> ->ghes_irq_func
>>>   ->ghes_proc
>>>     ->ghes_do_proc()
>>>       ->ghes_handle_aer()
>>>         ->aer_recover_work_func()
>>>           ->pcie_do_recovery()
>>>             ->aer_root_reset()
>>>
>>> and aer driver etc.  if aer wants to do some access might conflict
>>> with firmware(or
>>> firmware in embedded controller) should check _OSC_ etc first. 
>>> blindly issue
>>> PCI_ERR_ROOT_COMMAND  or clear PCI_ERR_ROOT_STATUS *likely*
>>> cause errors by error handling itself.
>>
>> If _OSC negotiation ends up with FW being in control of AER, that 
>> means OS is not in charge and should not be messing with AER I guess. 
>> That seems appropriate to me then.
> But APEI based notification is more like a hybrid approach (frimware 
> first detects the
> error and notifies OS). Since spec does not clarify what OS is allowed 
> to do, its bit of a
> gray area now. My point is, since firmware allows OS to process the 
> error by sending
> the notification, I think its OK to clear the status once the error is 
> handled.

I don’t disagree as long as AER is granted to the OS via _OSC. But if 
it’s not granted explicitly via _OSC even in the APEI case where 
it’s either an SCI or NMI and not an MSI, I’m unsure whether the OS 
should be touching those registers.

Sean

>>
>> Thanks,
>>
>> Sean
>>
>>
>>
>>>
>>> Thanks,
>>> Ethan
>>>
>>>>
>>>> On Fri, Oct 16, 2020 at 03:30:37PM -0500, Bjorn Helgaas wrote:
>>>>> [+to Jonathan]
>>>>>
>>>>> On Thu, Oct 15, 2020 at 05:11:10PM -0700, Sean V Kelley wrote:
>>>>>> From: Qiuxu Zhuo <qiuxu.zhuo@...el.com>
>>>>>>
>>>>>> When attempting error recovery for an RCiEP associated with an 
>>>>>> RCEC device,
>>>>>> there needs to be a way to update the Root Error Status, the 
>>>>>> Uncorrectable
>>>>>> Error Status and the Uncorrectable Error Severity of the parent 
>>>>>> RCEC.  In
>>>>>> some non-native cases in which there is no OS-visible device 
>>>>>> associated
>>>>>> with the RCiEP, there is nothing to act upon as the firmware is 
>>>>>> acting
>>>>>> before the OS.
>>>>>>
>>>>>> Add handling for the linked RCEC in AER/ERR while taking into 
>>>>>> account
>>>>>> non-native cases.
>>>>>>
>>>>>> Co-developed-by: Sean V Kelley <sean.v.kelley@...el.com>
>>>>>> Link: 
>>>>>> https://lore.kernel.org/r/20201002184735.1229220-12-seanvk.dev@oregontracks.org
>>>>>> Signed-off-by: Sean V Kelley <sean.v.kelley@...el.com>
>>>>>> Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@...el.com>
>>>>>> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
>>>>>> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
>>>>>> ---
>>>>>>  drivers/pci/pcie/aer.c | 53 
>>>>>> ++++++++++++++++++++++++++++++------------
>>>>>>  drivers/pci/pcie/err.c | 20 ++++++++--------
>>>>>>  2 files changed, 48 insertions(+), 25 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
>>>>>> index 65dff5f3457a..083f69b67bfd 100644
>>>>>> --- a/drivers/pci/pcie/aer.c
>>>>>> +++ b/drivers/pci/pcie/aer.c
>>>>>> @@ -1357,27 +1357,50 @@ static int aer_probe(struct pcie_device 
>>>>>> *dev)
>>>>>>   */
>>>>>>  static pci_ers_result_t aer_root_reset(struct pci_dev *dev)
>>>>>>  {
>>>>>> -   int aer = dev->aer_cap;
>>>>>> +   int type = pci_pcie_type(dev);
>>>>>> +   struct pci_dev *root;
>>>>>> +   int aer = 0;
>>>>>> +   int rc = 0;
>>>>>>     u32 reg32;
>>>>>> -   int rc;
>>>>>>
>>>>>> +   if (pci_pcie_type(dev) == PCI_EXP_TYPE_RC_END)
>>>>>
>>>>> "type == PCI_EXP_TYPE_RC_END"
>>>>>
>>>>>> +           /*
>>>>>> +            * The reset should only clear the Root 
>>>>>> Error Status
>>>>>> +            * of the RCEC. Only perform this for the
>>>>>> +            * native case, i.e., an RCEC is present.
>>>>>> +            */
>>>>>> +           root = dev->rcec;
>>>>>> +   else
>>>>>> +           root = dev;
>>>>>>
>>>>>> -   /* Disable Root's interrupt in response to error messages 
>>>>>> */
>>>>>> -   pci_read_config_dword(dev, aer + PCI_ERR_ROOT_COMMAND, 
>>>>>> &reg32);
>>>>>> -   reg32 &= ~ROOT_PORT_INTR_ON_MESG_MASK;
>>>>>> -   pci_write_config_dword(dev, aer + PCI_ERR_ROOT_COMMAND, 
>>>>>> reg32);
>>>>>> +   if (root)
>>>>>> +           aer = dev->aer_cap;
>>>>>>
>>>>>> -   rc = pci_bus_error_reset(dev);
>>>>>> -   pci_info(dev, "Root Port link has been reset\n");
>>>>>> +   if (aer) {
>>>>>> +           /* Disable Root's interrupt in response to 
>>>>>> error messages */
>>>>>> +           pci_read_config_dword(root, aer + 
>>>>>> PCI_ERR_ROOT_COMMAND, &reg32);
>>>>>> +           reg32 &= ~ROOT_PORT_INTR_ON_MESG_MASK;
>>>>>> +           pci_write_config_dword(root, aer + 
>>>>>> PCI_ERR_ROOT_COMMAND, reg32);
>>>>>
>>>>> Not directly related to *this* patch, but my assumption was that 
>>>>> in
>>>>> the APEI case, the firmware should retain ownership of the AER
>>>>> Capability, so the OS should not touch PCI_ERR_ROOT_COMMAND and
>>>>> PCI_ERR_ROOT_STATUS.
>>>>>
>>>>> But this code appears to ignore that ownership.  Jonathan, you 
>>>>> must
>>>>> have looked at this recently for 068c29a248b6 ("PCI/ERR: Clear 
>>>>> PCIe
>>>>> Device Status errors only if OS owns AER").  Do you have any 
>>>>> insight
>>>>> about this?
>>>>>
>>>>>> -   /* Clear Root Error Status */
>>>>>> -   pci_read_config_dword(dev, aer + PCI_ERR_ROOT_STATUS, 
>>>>>> &reg32);
>>>>>> -   pci_write_config_dword(dev, aer + PCI_ERR_ROOT_STATUS, 
>>>>>> reg32);
>>>>>> +           /* Clear Root Error Status */
>>>>>> +           pci_read_config_dword(root, aer + 
>>>>>> PCI_ERR_ROOT_STATUS, &reg32);
>>>>>> +           pci_write_config_dword(root, aer + 
>>>>>> PCI_ERR_ROOT_STATUS, reg32);
>>>>>>
>>>>>> -   /* Enable Root Port's interrupt in response to error 
>>>>>> messages */
>>>>>> -   pci_read_config_dword(dev, aer + PCI_ERR_ROOT_COMMAND, 
>>>>>> &reg32);
>>>>>> -   reg32 |= ROOT_PORT_INTR_ON_MESG_MASK;
>>>>>> -   pci_write_config_dword(dev, aer + PCI_ERR_ROOT_COMMAND, 
>>>>>> reg32);
>>>>>> +           /* Enable Root Port's interrupt in response 
>>>>>> to error messages */
>>>>>> +           pci_read_config_dword(root, aer + 
>>>>>> PCI_ERR_ROOT_COMMAND, &reg32);
>>>>>> +           reg32 |= ROOT_PORT_INTR_ON_MESG_MASK;
>>>>>> +           pci_write_config_dword(root, aer + 
>>>>>> PCI_ERR_ROOT_COMMAND, reg32);
>>>>>> +   }
>>>>>> +
>>>>>> +   if ((type == PCI_EXP_TYPE_RC_EC) || (type == 
>>>>>> PCI_EXP_TYPE_RC_END)) {
>>>>>> +           if (pcie_has_flr(root)) {
>>>>>> +                   rc = pcie_flr(root);
>>>>>> +                   pci_info(dev, "has been 
>>>>>> reset (%d)\n", rc);
>>>>>> +           }
>>>>>> +   } else {
>>>>>> +           rc = pci_bus_error_reset(root);
>>>>>
>>>>> Don't we want "dev" for both the FLR and pci_bus_error_reset()?  
>>>>> I
>>>>> think "root == dev" except when dev is an RCiEP.  When dev is an
>>>>> RCiEP, "root" is the RCEC (if present), and we want to reset the
>>>>> RCiEP, not the RCEC.
>>>>>
>>>>>> +           pci_info(dev, "Root Port link has been 
>>>>>> reset (%d)\n", rc);
>>>>>> +   }
>>>>>
>>>>> There are a couple changes here that I think should be split out.
>>>>>
>>>>> Based on my theory that when firmware retains control of AER, the 
>>>>> OS
>>>>> should not touch PCI_ERR_ROOT_COMMAND and PCI_ERR_ROOT_STATUS, and 
>>>>> any
>>>>> updates to them would have to be done by firmware before we get 
>>>>> here,
>>>>> I suggested reordering this:
>>>>>
>>>>>   - clear PCI_ERR_ROOT_COMMAND ROOT_PORT_INTR_ON_MESG_MASK
>>>>>   - do reset
>>>>>   - clear PCI_ERR_ROOT_STATUS (for APEI, presumably done by 
>>>>> firmware?)
>>>>>   - enable PCI_ERR_ROOT_COMMAND ROOT_PORT_INTR_ON_MESG_MASK
>>>>>
>>>>> to this:
>>>>>
>>>>>   - clear PCI_ERR_ROOT_COMMAND ROOT_PORT_INTR_ON_MESG_MASK
>>>>>   - clear PCI_ERR_ROOT_STATUS
>>>>>   - enable PCI_ERR_ROOT_COMMAND ROOT_PORT_INTR_ON_MESG_MASK
>>>>>   - do reset
>>>>>
>>>>> If my theory is correct, I think we should still reorder this, 
>>>>> but:
>>>>>
>>>>>   - It's a significant behavior change that deserves its own 
>>>>> patch so
>>>>>     we can document/bisect/revert.
>>>>>
>>>>>   - I'm not sure why we clear the PCI_ERR_ROOT_COMMAND error 
>>>>> reporting
>>>>>     bits.  In the new "clear COMMAND, clear STATUS, enable 
>>>>> COMMAND"
>>>>>     order, it looks superfluous.  There's no reason to disable 
>>>>> error
>>>>>     reporting while clearing the status bits.
>>>>>
>>>>>     The current "clear, reset, enable" order suggests that the 
>>>>> reset
>>>>>     might cause errors that we should ignore.  I don't know 
>>>>> whether
>>>>>     that's the case or not.  It dates from 6c2b374d7485 
>>>>> ("PCI-Express
>>>>>     AER implemetation: AER core and aerdriver"), which doesn't
>>>>>     elaborate.
>>>>>
>>>>>   - Should we also test for OS ownership of AER before touching
>>>>>     PCI_ERR_ROOT_STATUS?
>>>>>
>>>>>   - If we remove the PCI_ERR_ROOT_COMMAND fiddling (and I 
>>>>> tentatively
>>>>>     think we *should* unless we can justify it), that would 
>>>>> also
>>>>>     deserve its own patch.  Possibly (1) remove 
>>>>> PCI_ERR_ROOT_COMMAND
>>>>>     fiddling, (2) reorder PCI_ERR_ROOT_STATUS clearing and 
>>>>> reset, (3)
>>>>>     test for OS ownership of AER (?), (4) the rest of this 
>>>>> patch.
>>>>>
>>>>>>     return rc ? PCI_ERS_RESULT_DISCONNECT : 
>>>>>> PCI_ERS_RESULT_RECOVERED;
>>>>>>  }
>>>>>> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
>>>>>> index 7883c9791562..cbc5abfe767b 100644
>>>>>> --- a/drivers/pci/pcie/err.c
>>>>>> +++ b/drivers/pci/pcie/err.c
>>>>>> @@ -148,10 +148,10 @@ static int report_resume(struct pci_dev 
>>>>>> *dev, void *data)
>>>>>>
>>>>>>  /**
>>>>>>   * pci_walk_bridge - walk bridges potentially AER affected
>>>>>> - * @bridge:        bridge which may be a Port, an RCEC 
>>>>>> with associated RCiEPs,
>>>>>> - *         or an RCiEP associated with an RCEC
>>>>>> - * @cb:            callback to be called for each 
>>>>>> device found
>>>>>> - * @userdata:      arbitrary pointer to be passed to 
>>>>>> callback
>>>>>> + * @bridge   bridge which may be an RCEC with associated 
>>>>>> RCiEPs,
>>>>>> + *           or a Port.
>>>>>> + * @cb       callback to be called for each device found
>>>>>> + * @userdata arbitrary pointer to be passed to callback.
>>>>>>   *
>>>>>>   * If the device provided is a bridge, walk the subordinate 
>>>>>> bus, including
>>>>>>   * any bridged devices on buses under this bus.  Call the 
>>>>>> provided callback
>>>>>> @@ -164,8 +164,14 @@ static void pci_walk_bridge(struct pci_dev 
>>>>>> *bridge,
>>>>>>                         int (*cb)(struct 
>>>>>> pci_dev *, void *),
>>>>>>                         void *userdata)
>>>>>>  {
>>>>>> +   /*
>>>>>> +    * In a non-native case where there is no OS-visible 
>>>>>> reporting
>>>>>> +    * device the bridge will be NULL, i.e., no RCEC, no 
>>>>>> Downstream Port.
>>>>>> +    */
>>>>>>     if (bridge->subordinate)
>>>>>>             pci_walk_bus(bridge->subordinate, cb, 
>>>>>> userdata);
>>>>>> +   else if (bridge->rcec)
>>>>>> +           cb(bridge->rcec, userdata);
>>>>>>     else
>>>>>>             cb(bridge, userdata);
>>>>>>  }
>>>>>> @@ -194,12 +200,6 @@ pci_ers_result_t pcie_do_recovery(struct 
>>>>>> pci_dev *dev,
>>>>>>     pci_dbg(bridge, "broadcast error_detected message\n");
>>>>>>     if (state == pci_channel_io_frozen) {
>>>>>>             pci_walk_bridge(bridge, 
>>>>>> report_frozen_detected, &status);
>>>>>> -           if (type == PCI_EXP_TYPE_RC_END) {
>>>>>> -                   pci_warn(dev, "subordinate 
>>>>>> device reset not possible for RCiEP\n");
>>>>>> -                   status = 
>>>>>> PCI_ERS_RESULT_NONE;
>>>>>> -                   goto failed;
>>>>>> -           }
>>>>>> -
>>>>>>             status = reset_subordinates(bridge);
>>>>>>             if (status != PCI_ERS_RESULT_RECOVERED) {
>>>>>>                     pci_warn(bridge, 
>>>>>> "subordinate device reset failed\n");
>>>>>> -- 
>>>>>> 2.28.0
>>>>>>
> -- 
> Sathyanarayanan Kuppuswamy
> Linux Kernel Developer

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