Date:   Fri, 09 Oct 2020 12:48:07 -0700
From:   "Sean V Kelley" <sean.v.kelley@...el.com>
To:     "Bjorn Helgaas" <helgaas@...nel.org>
Cc:     "Sean V Kelley" <seanvk.dev@...gontracks.org>, bhelgaas@...gle.com,
        Jonathan.Cameron@...wei.com, rafael.j.wysocki@...el.com,
        ashok.raj@...el.com, tony.luck@...el.com,
        sathyanarayanan.kuppuswamy@...el.com, qiuxu.zhuo@...el.com,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 11/14] PCI/RCEC: Add RCiEP's linked RCEC to AER/ERR

On 9 Oct 2020, at 11:53, Sean V Kelley wrote:

> On 9 Oct 2020, at 11:34, Sean V Kelley wrote:
>
>> On 9 Oct 2020, at 11:26, Sean V Kelley wrote:
>>
>>> Hi Bjorn,
>>>
>>> On 9 Oct 2020, at 10:57, Bjorn Helgaas wrote:
>>>
>>>> On Fri, Oct 02, 2020 at 11:47:32AM -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. So 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>
>>>>> Signed-off-by: Sean V Kelley <sean.v.kelley@...el.com>
>>>>> Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@...el.com>
>>>>> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
>>>>> ---
>>>>>  drivers/pci/pcie/aer.c |  9 +++++----
>>>>>  drivers/pci/pcie/err.c | 39 
>>>>> ++++++++++++++++++++++++++++-----------
>>>>>  2 files changed, 33 insertions(+), 15 deletions(-)
>>>>>
>>>>> diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
>>>>> index 65dff5f3457a..dccdba60b5d9 100644
>>>>> --- a/drivers/pci/pcie/aer.c
>>>>> +++ b/drivers/pci/pcie/aer.c
>>>>> @@ -1358,17 +1358,18 @@ 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 rc = 0;
>>>>>  	u32 reg32;
>>>>> -	int rc;
>>>>> -
>>>>>
>>>>>  	/* 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);
>>>>>
>>>>> -	rc = pci_bus_error_reset(dev);
>>>>> -	pci_info(dev, "Root Port link has been reset\n");
>>>>> +	if (pci_pcie_type(dev) != PCI_EXP_TYPE_RC_EC) {
>>>>> +		rc = pci_bus_error_reset(dev);
>>>>> +		pci_info(dev, "Root Port link has been reset\n");
>>>>> +	}
>>>>>
>>>>>  	/* Clear Root Error Status */
>>>>>  	pci_read_config_dword(dev, aer + PCI_ERR_ROOT_STATUS, &reg32);
>>>>> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
>>>>> index 38abd7984996..956ad4c86d53 100644
>>>>> --- a/drivers/pci/pcie/err.c
>>>>> +++ b/drivers/pci/pcie/err.c
>>>>> @@ -149,7 +149,8 @@ static int report_resume(struct pci_dev *dev, 
>>>>> void *data)
>>>>>  /**
>>>>>   * pci_walk_bridge - walk bridges potentially AER affected
>>>>>   * @bridge   bridge which may be an RCEC with associated RCiEPs,
>>>>> - *           an RCiEP associated with an RCEC, or a Port.
>>>>> + *           or a Port.
>>>>> + * @dev      an RCiEP lacking an associated RCEC.
>>>>>   * @cb       callback to be called for each device found
>>>>>   * @userdata arbitrary pointer to be passed to callback.
>>>>>   *
>>>>> @@ -160,13 +161,20 @@ static int report_resume(struct pci_dev 
>>>>> *dev, void *data)
>>>>>   * If the device provided has no subordinate bus, call the 
>>>>> provided
>>>>>   * callback on the device itself.
>>>>>   */
>>>>> -static void pci_walk_bridge(struct pci_dev *bridge, int 
>>>>> (*cb)(struct pci_dev *, void *),
>>>>> +static void pci_walk_bridge(struct pci_dev *bridge, struct 
>>>>> pci_dev *dev,
>>>>> +			    int (*cb)(struct pci_dev *, void *),
>>>>>  			    void *userdata)
>>>>>  {
>>>>> -	if (bridge->subordinate)
>>>>> +	/*
>>>>> +	 * In a non-native case where there is no OS-visible reporting
>>>>> +	 * device the bridge will be NULL, i.e., no RCEC, no PORT.
>>>>> +	 */
>>>>> +	if (bridge && bridge->subordinate)
>>>>>  		pci_walk_bus(bridge->subordinate, cb, userdata);
>>>>> -	else
>>>>> +	else if (bridge)
>>>>>  		cb(bridge, userdata);
>>>>> +	else
>>>>> +		cb(dev, userdata);
>>>>>  }
>>>>>
>>>>>  static pci_ers_result_t flr_on_rciep(struct pci_dev *dev)
>>>>> @@ -196,16 +204,25 @@ pci_ers_result_t pcie_do_recovery(struct 
>>>>> pci_dev *dev,
>>>>>  	type = pci_pcie_type(dev);
>>>>>  	if (type == PCI_EXP_TYPE_ROOT_PORT ||
>>>>>  	    type == PCI_EXP_TYPE_DOWNSTREAM ||
>>>>> -	    type == PCI_EXP_TYPE_RC_EC ||
>>>>> -	    type == PCI_EXP_TYPE_RC_END)
>>>>> +	    type == PCI_EXP_TYPE_RC_EC)
>>>>>  		bridge = dev;
>>>>> +	else if (type == PCI_EXP_TYPE_RC_END)
>>>>> +		bridge = dev->rcec;
>>>>>  	else
>>>>>  		bridge = pci_upstream_bridge(dev);
>>>>>
>>>>>  	pci_dbg(dev, "broadcast error_detected message\n");
>>>>>  	if (state == pci_channel_io_frozen) {
>>>>> -		pci_walk_bridge(bridge, report_frozen_detected, &status);
>>>>> +		pci_walk_bridge(bridge, dev, report_frozen_detected, &status);
>>>>>  		if (type == PCI_EXP_TYPE_RC_END) {
>>>>> +			/*
>>>>> +			 * The callback only clears the Root Error Status
>>>>> +			 * of the RCEC (see aer.c). Only perform this for the
>>>>> +			 * native case, i.e., an RCEC is present.
>>>>> +			 */
>>>>> +			if (bridge)
>>>>> +				reset_subordinate_devices(bridge);
>>>>
>>>> Help me understand this.  There are lots of callbacks in this 
>>>> picture,
>>>> but I guess this "callback only clears Root Error Status" must 
>>>> refer
>>>> to aer_root_reset(), i.e., the reset_subordinate_devices pointer?
>>>
>>> The ‘bridge’ in this case will always be dev->rcec, the event 
>>> collector for the associated RC_END. And that’s what’s being 
>>> cleared in aer.c via aer_root_reset() as the callback. It’s also 
>>> being checked for native/non-native here.
>>>
>>>>
>>>> Of course, the caller of pcie_do_recovery() supplied that pointer.
>>>> And we can infer that it must be aer_root_reset(), not
>>>> dpc_reset_link(), because RCECs and RCiEPs are not allowed to
>>>> implement DPC.
>>>
>>> Correct.
>>>
>>>>
>>>> I wish we didn't have either this assumption about what
>>>> reset_subordinate_devices points to, or the assumption about what
>>>> aer_root_reset() does.  They both seem a little bit tenuous.
>>>
>>> Agree. It’s the relationship between the RC_END and the RC_EC.
>>>
>>>>
>>>> We already made aer_root_reset() smart enough to check for RCECs.  
>>>> Can
>>>> we put the FLR there, too?  Then we wouldn't have this weird 
>>>> situation
>>>> where reset_subordinate_devices() does a reset and clears error
>>>> status, EXCEPT for this case where it only clears error status and 
>>>> we
>>>> do the reset here?
>>>
>>> We could add the smarts to aer_root_reset() to check for an RC_END 
>>> in that callback and perform the clear there on its RC_EC. We just 
>>> wouldn’t map ‘bridge’ to dev->rcec for RC_END in 
>>> pcie_do_recovery() which would simplify things.
>>>
>>> Further, the FLR in the case of flr_on_rciep() below is specific to 
>>> the RCiEP itself. So it could be performed either in 
>>> aer_root_reset() or remain in the pcie_do_recovery().
>>>
>>> That should work.
>>>
>>> Sean
>>
>> Thinking more on this, you could still pass dev->rcec to the callback 
>> (eventually aer_root_reset()), but you won’t have the ability to 
>> handle the FLR there without the pointer to the RC_END. That’s why 
>> I suggested passing the RC_END and checking for its RC_EC in 
>> aer_root_reset() if you want to also handle FLR there too from below.
>
> Where you get into trouble is that you don’t want to do anything in 
> the non-native case and shouldn’t be going to the callback. So this 
> would add complexity to aer_root_reset() for checking on dev->rcec == 
> NULL…where before you never would have invoked 
> reset_subordinate_devices() in the non-native case.
>
>

Unmapping of bridge to dev->rcec in pcie_do_recovery() also causes 
problems for pci_walk_bridge() which pays attention to the non-native 
case, even making available the dev for when there is no ‘bridge’ 
like device.

I think we may be just shifting things elsewhere despite the constraints 
remaining the same. So while it should work, I believe that I prefer the 
current approach.

Sean



>>
>> Sean
>>
>>>
>>>
>>>>
>>>>>  			status = flr_on_rciep(dev);
>>>>>  			if (status != PCI_ERS_RESULT_RECOVERED) {
>>>>>  				pci_warn(dev, "function level reset failed\n");
>>>>> @@ -219,13 +236,13 @@ pci_ers_result_t pcie_do_recovery(struct 
>>>>> pci_dev *dev,
>>>>>  			}
>>>>>  		}
>>>>>  	} else {
>>>>> -		pci_walk_bridge(bridge, report_normal_detected, &status);
>>>>> +		pci_walk_bridge(bridge, dev, report_normal_detected, &status);
>>>>>  	}
>>>>>
>>>>>  	if (status == PCI_ERS_RESULT_CAN_RECOVER) {
>>>>>  		status = PCI_ERS_RESULT_RECOVERED;
>>>>>  		pci_dbg(dev, "broadcast mmio_enabled message\n");
>>>>> -		pci_walk_bridge(bridge, report_mmio_enabled, &status);
>>>>> +		pci_walk_bridge(bridge, dev, report_mmio_enabled, &status);
>>>>>  	}
>>>>>
>>>>>  	if (status == PCI_ERS_RESULT_NEED_RESET) {
>>>>> @@ -236,14 +253,14 @@ pci_ers_result_t pcie_do_recovery(struct 
>>>>> pci_dev *dev,
>>>>>  		 */
>>>>>  		status = PCI_ERS_RESULT_RECOVERED;
>>>>>  		pci_dbg(dev, "broadcast slot_reset message\n");
>>>>> -		pci_walk_bridge(bridge, report_slot_reset, &status);
>>>>> +		pci_walk_bridge(bridge, dev, report_slot_reset, &status);
>>>>>  	}
>>>>>
>>>>>  	if (status != PCI_ERS_RESULT_RECOVERED)
>>>>>  		goto failed;
>>>>>
>>>>>  	pci_dbg(dev, "broadcast resume message\n");
>>>>> -	pci_walk_bridge(bridge, report_resume, &status);
>>>>> +	pci_walk_bridge(bridge, dev, report_resume, &status);
>>>>>
>>>>>  	if (type == PCI_EXP_TYPE_ROOT_PORT ||
>>>>>  	    type == PCI_EXP_TYPE_DOWNSTREAM ||
>>>>> -- 
>>>>> 2.28.0
>>>>>

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