PCI/AER: Add ratelimits to PCI AER Documentation

Add ratelimits section for rationale and defaults.

[bhelgaas: note fatal errors are not ratelimited]

Signed-off-by: Karolina Stolarek <[email protected]>
Signed-off-by: Jon Pan-Doh <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>
Tested-by: Krzysztof Wilczyński <[email protected]>
Reviewed-by: Kuppuswamy Sathyanarayanan <[email protected]>
Acked-by: Paul E. McKenney <[email protected]>
Link: https://patch.msgid.link/[email protected]

Author: Jon Pan-Doh

Documentation/PCI/pcieaer-howto.rst

@@ -85,6 +85,18 @@ In the example, 'Requester ID' means the ID of the device that sent
 the error message to the Root Port. Please refer to PCIe specs for other
 fields.
 
+AER Ratelimits
+--------------
+
+Since error messages can be generated for each transaction, we may see
+large volumes of errors reported. To prevent spammy devices from flooding
+the console/stalling execution, messages are throttled by device and error
+type (correctable vs. non-fatal uncorrectable).  Fatal errors, including
+DPC errors, are not ratelimited.
+
+AER uses the default ratelimit of DEFAULT_RATELIMIT_BURST (10 events) over
+DEFAULT_RATELIMIT_INTERVAL (5 seconds).
+
 AER Statistics / Counters
 -------------------------