Subject: Re: linux-next: manual merge of the amdgpu tree with the pci tree

From: Stephen Rothwell <[email-masked]>
Date: Tue, 15 Dec 2020 07:34:31 +1100

Hi all,

On Tue, 8 Dec 2020 13:56:20 +1100 Stephen Rothwell <[email-masked]> wrote:
>
> Today's linux-next merge of the amdgpu tree got a conflict in:
> 
>   drivers/pci/pcie/err.c
> 
> between commits:
> 
>   8f1bbfbc3596 ("PCI/ERR: Rename reset_link() to reset_subordinates()")
>   0791721d8007 ("PCI/ERR: Use "bridge" for clarity in pcie_do_recovery()")
>   05e9ae19ab83 ("PCI/ERR: Add pci_walk_bridge() to pcie_do_recovery()")
> 
> from the pci tree and commit:
> 
>   36a8901e900a ("PCI/ERR: Fix reset logic in pcie_do_recovery() call")
> 
> from the amdgpu tree.
> 
> I fixed it up (I think - see below) and can carry the fix as
> necessary. This is now fixed as far as linux-next is concerned, but any
> non trivial conflicts should be mentioned to your upstream maintainer
> when your tree is submitted for merging.  You may also want to consider
> cooperating with the maintainer of the conflicting tree to minimise any
> particularly complex conflicts.
> 
> 
> diff --cc drivers/pci/pcie/err.c
> index 510f31f0ef6d,4a2735b70fa6..000000000000
> --- a/drivers/pci/pcie/err.c
> +++ b/drivers/pci/pcie/err.c
> @@@ -146,61 -146,49 +146,82 @@@ out
>   	return 0;
>   }
>   
>  +/**
>  + * pci_walk_bridge - walk bridges potentially AER affected
>  + * @bridge:	bridge which may be a Port, an RCEC, or an RCiEP
>  + * @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, e.g., an RCEC or RCiEP,
>  + * call the callback on the device itself.
>  + */
>  +static void pci_walk_bridge(struct pci_dev *bridge,
>  +			    int (*cb)(struct pci_dev *, void *),
>  +			    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_channel_state_t state,
>  +		pci_ers_result_t (*reset_subordinates)(struct pci_dev *pdev))
>   {
>  +	int type = pci_pcie_type(dev);
>  +	struct pci_dev *bridge;
>   	pci_ers_result_t status = PCI_ERS_RESULT_CAN_RECOVER;
>  -	struct pci_bus *bus;
>  +	struct pci_host_bridge *host = pci_find_host_bridge(dev->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.
>  +	 * If the error was detected by a Root Port, Downstream Port, RCEC,
>  +	 * or RCiEP, recovery runs on the device itself.  For Ports, that
>  +	 * also includes any subordinate devices.
>  +	 *
>  +	 * If it was detected by another device (Endpoint, etc), recovery
>  +	 * runs on the device and anything else under the same Port, i.e.,
>  +	 * everything under "bridge".
>   	 */
>  -	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;
>  +	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);
>   
>  -	pci_dbg(dev, "broadcast error_detected message\n");
>  +	pci_dbg(bridge, "broadcast error_detected message\n");
>   	if (state == pci_channel_io_frozen) {
>  -		pci_walk_bus(bus, report_frozen_detected, &status);
>  +		pci_walk_bridge(bridge, report_frozen_detected, &status);
> + 		/*
> + 		 * After resetting the link using reset_link() call, the
> + 		 * possible value of error status is either
> + 		 * PCI_ERS_RESULT_DISCONNECT (failure case) or
> + 		 * PCI_ERS_RESULT_NEED_RESET (success case).
> + 		 * So ignore the return value of report_error_detected()
> + 		 * call for fatal errors.
> + 		 *
> + 		 * In EDR mode, since AER and DPC Capabilities are owned by
> + 		 * firmware, reported_error_detected() will return error
> + 		 * status PCI_ERS_RESULT_NO_AER_DRIVER. Continuing
> + 		 * pcie_do_recovery() with error status as
> + 		 * PCI_ERS_RESULT_NO_AER_DRIVER will report recovery failure
> + 		 * irrespective of recovery status. But successful reset_link()
> + 		 * call usually recovers all fatal errors. So ignoring the
> + 		 * status result of report_error_detected() also helps EDR based
> + 		 * error recovery.
> + 		 */
>  -		status = reset_link(dev);
>  +		status = reset_subordinates(bridge);
> - 		if (status != PCI_ERS_RESULT_RECOVERED) {
> + 		if (status == PCI_ERS_RESULT_RECOVERED) {
> + 			status = PCI_ERS_RESULT_NEED_RESET;
> + 		} else {
> + 			status = PCI_ERS_RESULT_DISCONNECT;
>  -			pci_warn(dev, "link reset failed\n");
>  +			pci_warn(bridge, "subordinate device reset failed\n");
>   			goto failed;
>   		}
>   	} else {
> @@@ -215,13 -203,25 +236,25 @@@
>   
>   	if (status == PCI_ERS_RESULT_NEED_RESET) {
>   		/*
> - 		 * TODO: Should call platform-specific
> - 		 * functions to reset slot before calling
> - 		 * drivers' slot_reset callbacks?
> + 		 * TODO: Optimize the call to pci_reset_bus()
> + 		 *
> + 		 * There are two components to pci_reset_bus().
> + 		 *
> + 		 * 1. Do platform specific slot/bus reset.
> + 		 * 2. Save/Restore all devices in the bus.
> + 		 *
> + 		 * For hotplug capable devices and fatal errors,
> + 		 * device is already in reset state due to link
> + 		 * reset. So repeating platform specific slot/bus
> + 		 * reset via pci_reset_bus() call is redundant. So
> + 		 * can optimize this logic and conditionally call
> + 		 * pci_reset_bus().
>   		 */
> + 		pci_reset_bus(dev);
> + 
>   		status = PCI_ERS_RESULT_RECOVERED;
>  -		pci_dbg(dev, "broadcast slot_reset message\n");
>  -		pci_walk_bus(bus, report_slot_reset, &status);
>  +		pci_dbg(bridge, "broadcast slot_reset message\n");
>  +		pci_walk_bridge(bridge, report_slot_reset, &status);
>   	}
>   
>   	if (status != PCI_ERS_RESULT_RECOVERED)

Just a reminder that this conflict still exists (the amdgpu tree commit
is now 400b308d388a).

-- 
Cheers,
Stephen Rothwell