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Date:   Fri, 16 Oct 2020 18:45:47 -0700
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Bjorn Helgaas <helgaas@...nel.org>,
        Sean V Kelley <seanvk.dev@...gontracks.org>,
        Jonathan.Cameron@...wei.com
Cc:     bhelgaas@...gle.com, rafael.j.wysocki@...el.com,
        ashok.raj@...el.com, tony.luck@...el.com, qiuxu.zhuo@...el.com,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Sean V Kelley <sean.v.kelley@...el.com>,
        Christoph Hellwig <hch@....de>,
        Ethan Zhao <xerces.zhao@...il.com>,
        Sinan Kaya <okaya@...nel.org>, Keith Busch <kbusch@...nel.org>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.nkuppuswamy@...il.com>
Subject: Re: [PATCH v9 12/15] PCI/RCEC: Add RCiEP's linked RCEC to AER/ERR


On 10/16/20 3:29 PM, Bjorn Helgaas 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.]
This part is not very clear in ACPI spec or PCI firmware spec.

IMO, since AEPI notifies the OS about the error, then I guess
we are allowed to clear the PCI_ERR_ROOT_STATUS register
after handling the error (similar to EDR case).
>
> 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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