PCI/DPC: Log Error Source ID only when valid

PCI/DPC: Log Error Source ID only when valid

DPC Error Source ID is only valid when the DPC Trigger Reason indicates
that DPC was triggered due to reception of an ERR_NONFATAL or ERR_FATAL
Message (PCIe r6.0, sec 7.9.14.5).

When DPC was triggered by ERR_NONFATAL (PCI_EXP_DPC_STATUS_TRIGGER_RSN_NFE)
or ERR_FATAL (PCI_EXP_DPC_STATUS_TRIGGER_RSN_FE) from a downstream device,
log the Error Source ID (decoded into domain/bus/device/function).  Don't
print the source otherwise, since it's not valid.

For DPC trigger due to reception of ERR_NONFATAL or ERR_FATAL, the dmesg
logging changes:

  - pci 0000:00:01.0: DPC: containment event, status:0x000d source:0x0200
  - pci 0000:00:01.0: DPC: ERR_FATAL detected
  + pci 0000:00:01.0: DPC: containment event, status:0x000d, ERR_FATAL received from 0000:02:00.0

and when DPC triggered for other reasons, where DPC Error Source ID is
undefined, e.g., unmasked uncorrectable error:

  - pci 0000:00:01.0: DPC: containment event, status:0x0009 source:0x0200
  - pci 0000:00:01.0: DPC: unmasked uncorrectable error detected
  + pci 0000:00:01.0: DPC: containment event, status:0x0009: unmasked uncorrectable error detected

Previously the "containment event" message was at KERN_INFO and the
"%s detected" message was at KERN_WARNING.  Now the single message is at
KERN_WARNING.

Fixes: 26e515713342 ("PCI: Add Downstream Port Containment driver")
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://patch.msgid.link/20250522232339.1525671-3-helgaas@kernel.org