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Subject: Re: [PATCH v9 12/15] PCI/RCEC: Add RCiEP's linked RCEC to AER/ERR
To:     Sean V Kelley <sean.v.kelley@intel.com>,
        Ethan Zhao <xerces.zhao@gmail.com>
Cc:     Bjorn Helgaas <helgaas@kernel.org>,
        Sean V Kelley <seanvk.dev@oregontracks.org>,
        Jonathan.Cameron@huawei.com, Bjorn Helgaas <bhelgaas@google.com>,
        rafael.j.wysocki@intel.com, Ashok Raj <ashok.raj@intel.com>,
        tony.luck@intel.com, qiuxu.zhuo@intel.com,
        linux-pci <linux-pci@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Christoph Hellwig <hch@lst.de>, Sinan Kaya <okaya@kernel.org>,
        Keith Busch <kbusch@kernel.org>
References: <20201016203037.GA90074@bjorn-Precision-5520>
 <20201016222902.GA112659@bjorn-Precision-5520>
 <CAKF3qh3NDvQAwb922faHgja+YoDydCtg5sugEQ8T2ti+3WSn5Q@mail.gmail.com>
 <4F54EEC0-3933-4A2E-87BC-23FABECB0C0A@intel.com>
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@linux.intel.com>
Message-ID: <240932c3-2cf4-5fbd-9cda-520bbd953fa6@linux.intel.com>
Date:   Mon, 19 Oct 2020 11:59:29 -0700
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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@kernel.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.
>
> 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@intel.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@intel.com>
>>>>> Link: https://lore.kernel.org/r/20201002184735.1229220-12-seanvk.dev@oregontracks.org
>>>>> Signed-off-by: Sean V Kelley <sean.v.kelley@intel.com>
>>>>> Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
>>>>> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
>>>>> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.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