Date:   Sat, 17 Oct 2020 09:14:40 -0700
From:   "Sean V Kelley" <sean.v.kelley@...el.com>
To:     "Bjorn Helgaas" <helgaas@...nel.org>
Cc:     "Sean V Kelley" <seanvk.dev@...gontracks.org>,
        Jonathan.Cameron@...wei.com, bhelgaas@...gle.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 v9 12/15] PCI/RCEC: Add RCiEP's linked RCEC to AER/ERR

On 16 Oct 2020, at 13:30, 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"

Right, I merged your suggested changes which added the type. Will 
correct.

>
>> +		/*
>> +		 * 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.

Right, when I did the goto in the earlier incarnation, I always set root 
to dev at the start and in the merge it needs to be dev always except 
for the RC_END where RCEC exists. Will change without bringing back the 
goto…

+       struct pci_dev *root = dev;

…

+non_native:
+       if ((type == PCI_EXP_TYPE_RC_EC) || (type ==
PCI_EXP_TYPE_RC_END)) {
+               rc = flr_on_rc(root);
+               pci_info(dev, "has been reset (%d)\n", rc);
+       } else {
+               rc = pci_bus_error_reset(root);
+               pci_info(dev, "Root Port link has been reset (%d)\n",
rc);
+       }


>
>> +		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.

You’ve highlighted some good questions.

I think we should remove the fiddling until we have a clearer picture 
and put that into its own patch.

Sean
>
>>  	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
>>

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