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-rw-r--r--Documentation/networking/timestamping.txt7
1 files changed, 7 insertions, 0 deletions
diff --git a/Documentation/networking/timestamping.txt b/Documentation/networking/timestamping.txt
index 5f0922613f1a..a977339fbe0a 100644
--- a/Documentation/networking/timestamping.txt
+++ b/Documentation/networking/timestamping.txt
@@ -359,6 +359,13 @@ the requested fine-grained filtering for incoming packets is not
supported, the driver may time stamp more than just the requested types
of packets.
+Drivers are free to use a more permissive configuration than the requested
+configuration. It is expected that drivers should only implement directly the
+most generic mode that can be supported. For example if the hardware can
+support HWTSTAMP_FILTER_V2_EVENT, then it should generally always upscale
+HWTSTAMP_FILTER_V2_L2_SYNC_MESSAGE, and so forth, as HWTSTAMP_FILTER_V2_EVENT
+is more generic (and more useful to applications).
+
A driver which supports hardware time stamping shall update the struct
with the actual, possibly more permissive configuration. If the
requested packets cannot be time stamped, then nothing should be