Date:   Fri, 25 Sep 2020 16:14:07 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Sean V Kelley <seanvk.dev@...gontracks.org>
Cc:     bhelgaas@...gle.com, Jonathan.Cameron@...wei.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,
        Sean V Kelley <sean.v.kelley@...el.com>,
        Sinan Kaya <okaya@...nel.org>
Subject: Re: [PATCH v6 04/10] PCI/AER: Extend AER error handling to RCECs

[+cc Sinan, who's been reviewing changes in this area (thanks, Sinan!)]

On Tue, Sep 22, 2020 at 02:38:53PM -0700, Sean V Kelley 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 non-native
> handling. 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 non-native 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, which in turn references its associated RCEC.
> 
> A new walk function pci_bridge_walk(), similar to pci_bus_walk(),
> is provided that takes a pci_dev instead of a bus. If that bridge
> corresponds to a downstream port it will walk the subordinate bus of
> that bridge. If the device 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>

I like this patch.  I think there are a few things that could be
peeled off as "no functional change" preliminary patches to make the
important changes more obvious in the "money patch".

> ---
>  drivers/pci/pci.h      |  2 +-
>  drivers/pci/pcie/err.c | 77 +++++++++++++++++++++++++++++++-----------
>  2 files changed, 59 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 83670a6425d8..7b547fc3679a 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -575,7 +575,7 @@ static inline int pci_dev_specific_disable_acs_redir(struct pci_dev *dev)
>  /* PCI error reporting and recovery */
>  pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>  			pci_channel_state_t state,
> -			pci_ers_result_t (*reset_link)(struct pci_dev *pdev));
> +			pci_ers_result_t (*reset_subordinate_devices)(struct pci_dev *pdev));
>  
>  bool pcie_wait_for_link(struct pci_dev *pdev, bool active);
>  #ifdef CONFIG_PCIEASPM
> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
> index c543f419d8f9..e575fa6cee63 100644
> --- a/drivers/pci/pcie/err.c
> +++ b/drivers/pci/pcie/err.c
> @@ -146,38 +146,73 @@ static int report_resume(struct pci_dev *dev, void *data)
>  	return 0;
>  }
>  
> +/**
> + * pci_bridge_walk - walk bridges potentially AER affected
> + * @bridge   bridge 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 bridge, 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.
> + */
> +static void pci_bridge_walk(struct pci_dev *bridge, int (*cb)(struct pci_dev *, void *),

Maybe call this pci_walk_bridge() so it's the same order as the
existing pci_walk_bus(), unless there's some reason to be different.

> +			    void *userdata)
> +{
> +	if (bridge->subordinate)
> +		pci_walk_bus(bridge->subordinate, cb, userdata);
> +	else
> +		cb(bridge, userdata);
> +}
> +
>  pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>  			pci_channel_state_t state,
> -			pci_ers_result_t (*reset_link)(struct pci_dev *pdev))
> +			pci_ers_result_t (*reset_subordinate_devices)(struct pci_dev *pdev))

The rename to "reset_subordinate_devices" seems separable, since it
doesn't change the interface.

>  {
>  	pci_ers_result_t status = PCI_ERS_RESULT_CAN_RECOVER;
> -	struct pci_bus *bus;
> +	struct pci_dev *bridge;
> +	int type;
>  
>  	/*
> -	 * Error recovery runs on all subordinates of the first downstream port.
> -	 * If the downstream port detected the error, it is cleared at the end.
> +	 * Error recovery runs on all subordinates of the first downstream
> +	 * bridge. If the downstream bridge 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))
> -		dev = dev->bus->self;
> -	bus = dev->subordinate;
> +	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)
> +		bridge = dev;
> +	else
> +		bridge = pci_upstream_bridge(dev);

This makes it much easier to read, thank you.  I think the addition of
"type", rename of "dev" to "bridge", the inversion of the condition
(major improvement, thanks again), and use of pci_upstream_bridge()
instead of dev->bus->self might also be separable?

Of course, you'd have to add the RC_EC and RC_END cases later, in the
money patch, but that's a good thing because it won't get lost in all
the other things being changed.

>  	pci_dbg(dev, "broadcast error_detected message\n");
>  	if (state == pci_channel_io_frozen) {
> -		pci_walk_bus(bus, report_frozen_detected, &status);
> -		status = reset_link(dev);
> +		pci_bridge_walk(bridge, report_frozen_detected, &status);
> +		if (type == PCI_EXP_TYPE_RC_END) {
> +			pci_warn(dev, "link reset not possible for RCiEP\n");
> +			status = PCI_ERS_RESULT_NONE;
> +			goto failed;
> +		}
> +
> +		status = reset_subordinate_devices(bridge);
>  		if (status != PCI_ERS_RESULT_RECOVERED) {
> -			pci_warn(dev, "link reset failed\n");
> +			pci_warn(dev, "subordinate device reset failed\n");
>  			goto failed;
>  		}
>  	} else {
> -		pci_walk_bus(bus, report_normal_detected, &status);
> +		pci_bridge_walk(bridge, 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_bridge_walk(bridge, report_mmio_enabled, &status);
>  	}
>  
>  	if (status == PCI_ERS_RESULT_NEED_RESET) {
> @@ -188,18 +223,22 @@ 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_bridge_walk(bridge, 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);
> -
> -	if (pcie_aer_is_native(dev))
> -		pcie_clear_device_status(dev);
> -	pci_aer_clear_nonfatal_status(dev);
> +	pci_bridge_walk(bridge, report_resume, &status);
> +
> +	if (type == PCI_EXP_TYPE_ROOT_PORT ||
> +	    type == PCI_EXP_TYPE_DOWNSTREAM ||
> +	    type == PCI_EXP_TYPE_RC_EC) {

Addition of this check also seems worthy of a separate patch (for just
root ports and downstream ports first, then RC_EC being added later).
That would make a convenient place to explain why we need the change.
I think it's *correct*; it just gets lost in the noise and not even
mentioned when it's done as part of one big patch.

> +		if (pcie_aer_is_native(bridge))
> +			pcie_clear_device_status(bridge);
> +		pci_aer_clear_nonfatal_status(bridge);
> +	}
>  	pci_info(dev, "device recovery successful\n");
>  	return status;
>  
> -- 
> 2.28.0
> 

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