Date:   Mon, 27 Jul 2020 07:58:59 -0700
From:   "Sean V Kelley" <sean.v.kelley@...el.com>
To:     "Jonathan Cameron" <Jonathan.Cameron@...wei.com>
Cc:     bhelgaas@...gle.com, rjw@...ysocki.net, ashok.raj@...nel.org,
        tony.luck@...el.com, sathyanarayanan.kuppuswamy@...ux.intel.com,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 4/9] PCI/AER: Extend AER error handling to RCECs

On 27 Jul 2020, at 4:00, Jonathan Cameron wrote:

> On Fri, 24 Jul 2020 10:22:18 -0700
> Sean V Kelley <sean.v.kelley@...el.com> wrote:
>
>> From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
>>
>> Currently the kernel does not handle AER errors for Root Complex 
>> integrated
>> End Points (RCiEPs)[0]. These devices sit on a root bus within the 
>> Root Complex
>> (RC). AER handling is performed by a Root Complex Event Collector 
>> (RCEC) [1]
>> which is a effectively a type of RCiEP on the same root bus.
>>
>> For an RCEC (technically not a Bridge), error messages "received" 
>> from
>> associated RCiEPs must be enabled for "transmission" in order to 
>> cause a
>> System Error via the Root Control register or (when the Advanced 
>> Error
>> Reporting Capability is present) reporting via the Root Error Command
>> register and logging in the Root Error Status register and Error 
>> Source
>> Identification register.
>>
>> In addition to the defined OS level handling of the reset flow for 
>> the
>> associated RCiEPs of an RCEC, it is possible to also have a firmware 
>> first
>> model. In that case there is no need to take any actions on the RCEC 
>> because
>> the firmware is responsible for them. This is true where APEI [2] is 
>> used
>> to report the AER errors via a GHES[v2] HEST entry [3] and relevant
>> AER CPER record [4] and Firmware First handling is in use.
>>
>> We effectively end up with two different types of discovery for
>> purposes of handling AER errors:
>>
>> 1) Normal bus walk - we pass the downstream port above a bus to which
>> the device is attached and it walks everything below that point.
>>
>> 2) An RCiEP with no visible association with an RCEC as there is no 
>> need to
>> walk devices. In that case, the flow is to just call the callbacks 
>> for the actual
>> device.
>>
>> A new walk function, similar to pci_bus_walk is provided that takes a 
>> pci_dev
>> instead of a bus. If that dev corresponds to a downstream port it 
>> will walk
>> the subordinate bus of that downstream port. If the dev does not then 
>> it
>> will call the function on that device alone.
>>
>> [0] ACPI PCI Express Base Specification 5.0-1 1.3.2.3 Root Complex 
>> Integrated
>>     Endpoint Rules.
>> [1] ACPI PCI Express Base Specification 5.0-1 6.2 Error Signalling 
>> and Logging
>> [2] ACPI Specification 6.3 Chapter 18 ACPI Platform Error Interface 
>> (APEI)
>> [3] ACPI Specification 6.3 18.2.3.7 Generic Hardware Error Source
>> [4] UEFI Specification 2.8, N.2.7 PCI Express Error Section
>>
>> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
>> Signed-off-by: Sean V Kelley <sean.v.kelley@...el.com>
>> ---
>> Changes since v2 [1]:
>>
>> - Renamed to pci_walk_dev_affected() to reflect the aer affected 
>> devices
> Make sense.
>
>> - Localized to err.c and made static
>
> Makes sense.
>
>> - Added check for RCEC to reflect
> That comment probably needs a bit more...

Will add to the details.

>
>> - Tightened up commit log from earlier inquiry focused RFC
> Cool.
>
>
> Looks good to me and I like the new naming.
>
> A few really trivial tidy ups suggested for things that were less than 
> neat in my patch.
>
> Jonathan
>
>>
>> [1] 
>> https://lore.kernel.org/linux-pci/20200622114402.892798-1-Jonathan.Cameron@huawei.com/
>> ---
>>  drivers/pci/pcie/err.c | 55 
>> ++++++++++++++++++++++++++++++++++--------
>>  1 file changed, 45 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
>> index 14bb8f54723e..044df004f20b 100644
>> --- a/drivers/pci/pcie/err.c
>> +++ b/drivers/pci/pcie/err.c
>> @@ -146,38 +146,69 @@ static int report_resume(struct pci_dev *dev, 
>> void *data)
>>  	return 0;
>>  }
>>
>> +/** pci_walk_dev_affected - walk devices potentially AER affected
> /**
>  * pci_walk_dev_affected
>
> There is a bit of a mixture in pci files between the two styles, but
> I'm fairly sure kernel-doc is supposed to be as I'm suggesting
> (I had this wrong due to cut and paste in earlier version!)

Will fix.

>
>> + *  @dev      device which may be an RCEC with associated RCiEPs,
>> + *            an RCiEP associated with an RCEC, 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 port, walk the subordinate bus,
>> + *  including any bridged devices on buses under this bus.
>> + *  Call the provided callback on each device found.
>> + *
>> + *  If the device provided has no subordinate bus, call the provided
>> + *  callback on the device itself.
>> + *
>
> I also had an ugly pointless newline here. oops :)

Will fix.

Thanks,

Sean

>
>> + */
>> +static void pci_walk_dev_affected(struct pci_dev *dev, int 
>> (*cb)(struct pci_dev *, void *),
>> +				  void *userdata)
>> +{
>> +	if (dev->subordinate) {
>> +		pci_walk_bus(dev->subordinate, cb, userdata);
>> +	} else {
>> +		cb(dev, userdata);
>> +	}
>> +}
>> +
>>  pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>>  			enum pci_channel_state state,
>>  			pci_ers_result_t (*reset_link)(struct pci_dev *pdev))
>>  {
>>  	pci_ers_result_t status = PCI_ERS_RESULT_CAN_RECOVER;
>> -	struct pci_bus *bus;
>>
>>  	/*
>>  	 * Error recovery runs on all subordinates of the first downstream 
>> port.
>>  	 * If the downstream port detected the error, it is cleared at the 
>> end.
>> +	 * For RCiEPs we should reset just the RCiEP itself.
>>  	 */
>>  	if (!(pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT ||
>> -	      pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM))
>> +	      pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM ||
>> +	      pci_pcie_type(dev) == PCI_EXP_TYPE_RC_END ||
>> +	      pci_pcie_type(dev) == PCI_EXP_TYPE_RC_EC))
>>  		dev = dev->bus->self;
>> -	bus = dev->subordinate;
>>
>>  	pci_dbg(dev, "broadcast error_detected message\n");
>>  	if (state == pci_channel_io_frozen) {
>> -		pci_walk_bus(bus, report_frozen_detected, &status);
>> +		pci_walk_dev_affected(dev, report_frozen_detected, &status);
>> +		if (pci_pcie_type(dev) == PCI_EXP_TYPE_RC_END) {
>> +			pci_warn(dev, "link reset not possible for RCiEP\n");
>> +			status = PCI_ERS_RESULT_NONE;
>> +			goto failed;
>> +		}
>> +
>>  		status = reset_link(dev);
>>  		if (status != PCI_ERS_RESULT_RECOVERED) {
>>  			pci_warn(dev, "link reset failed\n");
>>  			goto failed;
>>  		}
>>  	} else {
>> -		pci_walk_bus(bus, report_normal_detected, &status);
>> +		pci_walk_dev_affected(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_bus(bus, report_mmio_enabled, &status);
>> +		pci_walk_dev_affected(dev, report_mmio_enabled, &status);
>>  	}
>>
>>  	if (status == PCI_ERS_RESULT_NEED_RESET) {
>> @@ -188,17 +219,21 @@ 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_bus(bus, report_slot_reset, &status);
>> +		pci_walk_dev_affected(dev, report_slot_reset, &status);
>>  	}
>>
>>  	if (status != PCI_ERS_RESULT_RECOVERED)
>>  		goto failed;
>>
>>  	pci_dbg(dev, "broadcast resume message\n");
>> -	pci_walk_bus(bus, report_resume, &status);
>> +	pci_walk_dev_affected(dev, report_resume, &status);
>>
>> -	pci_aer_clear_device_status(dev);
>> -	pci_aer_clear_nonfatal_status(dev);
>> +	if ((pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT ||
>> +	     pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM ||
>> +	     pci_pcie_type(dev) == PCI_EXP_TYPE_RC_EC)) {
>> +		pci_aer_clear_device_status(dev);
>> +		pci_aer_clear_nonfatal_status(dev);
>> +	}
>>  	pci_info(dev, "device recovery successful\n");
>>  	return status;
>>

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