[PATCH 3/4] PCI/ERR: Amend documentation with DPC and AER specifics

[Lukas Wunner]

Amend the documentation on PCI error recovery with specifics about
Downstream Port Containment and Advanced Error Reporting:

* Explain that with DPC, devices are inaccessible upon an error (similar
  to EEH on powerpc) and do not become accessible until the link is
  re-enabled.

* Explain that with AER, although devices may already be accessible in the
  ->error_detected() callback, accesses should be deferred to the
  ->mmio_enabled() callback for compatibility with EEH on powerpc.

Signed-off-by: Lukas Wunner <lukas at wunner.de>
---
 Documentation/PCI/pci-error-recovery.rst | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/Documentation/PCI/pci-error-recovery.rst b/Documentation/PCI/pci-error-recovery.rst
index d5c661baa87f..c88c304b2103 100644
--- a/Documentation/PCI/pci-error-recovery.rst
+++ b/Documentation/PCI/pci-error-recovery.rst
@@ -122,6 +122,10 @@ A PCI bus error is detected by the PCI hardware.  On powerpc, the slot
 is isolated, in that all I/O is blocked: all reads return 0xffffffff,
 all writes are ignored.
 
+Similarly, on platforms supporting Downstream Port Containment
+(PCIe r7.0 sec 6.2.11), the link to the sub-hierarchy with the
+faulting device is disabled. Any device in the sub-hierarchy
+becomes inaccessible.
 
 STEP 1: Notification
 --------------------
@@ -204,6 +208,23 @@ link reset was performed by the HW. If the platform can't just re-enable IOs
 without a slot reset or a link reset, it will not call this callback, and
 instead will have gone directly to STEP 3 (Link Reset) or STEP 4 (Slot Reset)
 
+.. note::
+
+   On platforms supporting Advanced Error Reporting (PCIe r7.0 sec 6.2),
+   the faulting device may already be accessible in STEP 1 (Notification).
+   Drivers should nevertheless defer accesses to STEP 2 (MMIO Enabled)
+   to be compatible with EEH on powerpc.
+
+   On platforms supporting Downstream Port Containment, the link to the
+   sub-hierarchy with the faulting device is re-enabled in STEP 3 (Link
+   Reset). Hence devices in the sub-hierarchy are inaccessible until
+   STEP 4 (Slot Reset).
+
+   For errors such as Surprise Down (PCIe r7.0 sec 6.2.7), the device
+   may not even be accessible in STEP 4 (Slot Reset). Drivers can detect
+   accessibility by checking whether reads from the device return all 1's
+   (PCI_POSSIBLE_ERROR()).
+
 .. note::
 
    The following is proposed; no platform implements this yet:
-- 
2.47.2