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From:   "Sean V Kelley" <sean.v.kelley@intel.com>
To:     "Bjorn Helgaas" <helgaas@kernel.org>
Cc:     "Sean V Kelley" <seanvk.dev@oregontracks.org>, bhelgaas@google.com,
        Jonathan.Cameron@huawei.com, rafael.j.wysocki@intel.com,
        ashok.raj@intel.com, tony.luck@intel.com,
        sathyanarayanan.kuppuswamy@intel.com, qiuxu.zhuo@intel.com,
        linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v8 11/14] PCI/RCEC: Add RCiEP's linked RCEC to AER/ERR
Date:   Fri, 09 Oct 2020 11:26:14 -0700
Message-ID: <41B2B0A9-80B0-41DA-9FF3-A5D9465E6E08@intel.com>
In-Reply-To: <20201009175745.GA3489710@bjorn-Precision-5520>
References: <20201009175745.GA3489710@bjorn-Precision-5520>
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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@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. 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@intel.com>
>> Signed-off-by: Sean V Kelley <sean.v.kelley@intel.com>
>> Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
>> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.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


>
>>  			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
>>