Re: [PATCH v2] PCI/AER: Add support for reset of RCiEPs for APEI/Firmware first reporting only

["Kuppuswamy, Sathyanarayanan" <sathyanarayanan.kuppuswamy@linux.intel.com>]

Hi, Jonathan,

On 6/22/20 4:44 AM, Jonathan Cameron wrote:
> Was previously: PCI/AER: Add partial initial supprot for RCiEPs using RCEC or
> firmware first.
> 
> Currently the kernel does not handle AER errors for Root Complex integrated
> End Points (RCiEPs)[0].
This patch makes pcie_do_recovery() aware of RCEC and RCiEP. But, did
you add support to receive IRQ for error detected in RCEC?
   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.
> 
> This code will only perform the correct reset flow for the case where 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.
> 
> As there is no current RCEC driver support, it should not be possible to get
> to this code via any routes other than the one above. Hence appropriate RCEC
> handling can be added when the RCEC driver support is ready.
> 
> The error handling is different from a normal PCIe End Point because:
> 
> 1) There is no downstream port above an RCiEP as these devices sit on a root
>     bus.
> 
> 2) In general, it makes little sense to reset other devices on on the same
>     root bus.  For error handling outside the of the root complex (RC) an AER
>     error will indicate that all the topology below the physical link, which
>     the error is related to, will need to be reset as they share a common
>     path to the host.  For an RCiEP there is no such defined shared path
>     relationship with other elements on the root bus.
> 
> 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.   This function allows us to
> avoid adding special cases to the majority of the error handling.
> 
> Open questions:
> 
> 1. Are we better protecting against link reset for an RCiEP in here or
>     should we put the check in the link reset functions?
> 
> 2. If we were to get a stupid firmware record with the relevant reset flag
>     set to trigger a link reset, what is the correct response?  For now I
>     try to report that we haven't done anything and print a warning.
> 
> 3. Naming of pci_walk_below_dev is rather unsatisfying. Any better ideas?
> 
> 4. pci_walk_below_dev is perhaps not of general utility. Shall I make it local
>     in err.c?  If not would a precursor patch for that be preferred?
> 
> Testing has been performed via error injection on a QEMU platform as that lets
> me create a wide range of topologies and report errors at any chosen location.
> Currently I have no plans to upstream this injection support, but am happy to
> share if useful to others.
> 
> [0] ACPI PCI Express Base Specification 4.0 1.3.2.3 Root Complex Integrated
>      Endpoint Rules.
> [1] ACPI PCI Express Base Specification 4.0 6.2 Error Signalling and Logging
> [2] ACPI Specification 6.3 Chapter 18 ACPI Platform Error Interface (APEI)
> [3] ACPI Sepcification 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@huawei.com>
> ---
> Changes since v1:
> * Separated from the largely unrelated fix so the two can move forwards separately.
> * Instead of separate path for RCiEP handling use the method suggested by Bjorn
>    and Sathyanarayanan with an adjusted pci_bus_walk.
> 
> Thanks all for reviews of V1.
>    
>   drivers/pci/bus.c      | 28 ++++++++++++++++++++++++++++
>   drivers/pci/pcie/err.c | 29 +++++++++++++++++++----------
>   include/linux/pci.h    |  2 ++
>   3 files changed, 49 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
> index 8e40b3e6da77..7cbe1ed2db3d 100644
> --- a/drivers/pci/bus.c
> +++ b/drivers/pci/bus.c
> @@ -411,6 +411,34 @@ void pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
>   }
>   EXPORT_SYMBOL_GPL(pci_walk_bus);
>   
> +/** pci_walk_below_dev - walk devices below (or on) another device
> + *  @dev      device for which we should walk below, include device when not 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 hs no subordinate bus, call the provided
> + *  callback on the device itself.
> + *
> + */
> +void pci_walk_below_dev(struct pci_dev *dev, int (*cb)(struct pci_dev *, void *),
> +			void *userdata)
> +{
> +	struct pci_bus *bus;
> +
> +	if (dev->subordinate) {
> +		bus = dev->subordinate;
> +		pci_walk_bus(bus, cb, userdata);
> +	} else {
> +		cb(dev, userdata);
> +	}
> +}
> +EXPORT_SYMBOL_GPL(pci_walk_below_dev);
> +
>   struct pci_bus *pci_bus_get(struct pci_bus *bus)
>   {
>   	if (bus)
> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
> index 14bb8f54723e..fa08b1cc3d96 100644
> --- a/drivers/pci/pcie/err.c
> +++ b/drivers/pci/pcie/err.c
> @@ -151,33 +151,39 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>   			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))
>   		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_below_dev(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_below_dev(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_below_dev(dev, report_mmio_enabled, &status);
>   	}
>   
>   	if (status == PCI_ERS_RESULT_NEED_RESET) {
> @@ -188,17 +194,20 @@ 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_below_dev(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_below_dev(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_aer_clear_device_status(dev);
> +		pci_aer_clear_nonfatal_status(dev);
> +	}
>   	pci_info(dev, "device recovery successful\n");
>   	return status;
>   
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index c79d83304e52..538bf0a76d33 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1411,6 +1411,8 @@ int pci_scan_bridge(struct pci_bus *bus, struct pci_dev *dev, int max,
>   
>   void pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
>   		  void *userdata);
> +void pci_walk_below_dev(struct pci_dev *dev, int (*cb)(struct pci_dev *, void *),
> +			void *userdata);
>   int pci_cfg_space_size(struct pci_dev *dev);
>   unsigned char pci_bus_max_busnr(struct pci_bus *bus);
>   void pci_setup_bridge(struct pci_bus *bus);
> 

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer