clarify implementation of ethtool's get_ts_info op

[firefly-linux-kernel-4.4.55.git] / Documentation / networking / timestamping.txt

diff --git a/Documentation/networking/timestamping.txt b/Documentation/networking/timestamping.txt
index 5f0922613f1a8db7963fe3c44d21280d7290d84e..a977339fbe0a50d94877fdb8d9f2e8d902699612 100644 (file)
--- 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