Help YNL decode the values for input-xfrm by defining
the possible values in the spec. Don't define "no change"
as it's an IOCTL artifact with no use in Netlink.

With this change on mlx5 input-xfrm gets decoded:

 # ynl --family ethtool --dump rss-get
 [{'header': {'dev-index': 2, 'dev-name': 'eth0'},
   'hfunc': 1,
   'hkey': b'V\xa8\xf9\x9 ...',
   'indir': [0, 1, ... ],
   'input-xfrm': {'sym-or-xor'},                         <<<
   'flow-hash': {'ah4': {'ip-dst', 'ip-src'},
                 'ah6': {'ip-dst', 'ip-src'},
                 'esp4': {'ip-dst', 'ip-src'},
                 'esp6': {'ip-dst', 'ip-src'},
                 'ip4': {'ip-dst', 'ip-src'},
                 'ip6': {'ip-dst', 'ip-src'},
                 'tcp4': {'l4-b-0-1', 'ip-dst', 'l4-b-2-3', 'ip-src'},
                 'tcp6': {'l4-b-0-1', 'ip-dst', 'l4-b-2-3', 'ip-src'},
                 'udp4': {'l4-b-0-1', 'ip-dst', 'l4-b-2-3', 'ip-src'},
                 'udp6': {'l4-b-0-1', 'ip-dst', 'l4-b-2-3', 'ip-src'}}
 }]

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
v3:
 - make input xfrm a flags field
v2:
 - adjust the test to decoded values
---
 Documentation/netlink/specs/ethtool.yaml      | 21 +++++++++++++++++++
 .../drivers/net/hw/rss_input_xfrm.py          |  6 +++---
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/Documentation/netlink/specs/ethtool.yaml b/Documentation/netlink/specs/ethtool.yaml
index aa55fc9068e1..d0a9c4120a19 100644
--- a/Documentation/netlink/specs/ethtool.yaml
+++ b/Documentation/netlink/specs/ethtool.yaml
@@ -158,6 +158,26 @@ c-version-name: ethtool-genl-version
       -
         name: pse-event-sw-pw-control-error
         doc: PSE faced an error managing the power control from software
+  -
+    name: input-xfrm
+    doc: RSS hash function transformations.
+    type: flags
+    enum-name:
+    name-prefix: rxh-xfrm-
+    header: linux/ethtool.h
+    entries:
+      -
+        name: sym-xor
+        doc: >-
+          XOR the corresponding source and destination fields of each specified
+          protocol. Both copies of the XOR'ed fields are fed into the RSS and
+          RXHASH calculation. Note that this XORing reduces the input set
+          entropy and could be exploited to reduce the RSS queue spread.
+      -
+        name: sym-or-xor
+        doc: >-
+          Similar to SYM_XOR, except that one copy of the XOR'ed fields is
+          replaced by an OR of the same fields.
   -
     name: rxfh-fields
     name-prefix: rxh-
@@ -1621,6 +1641,7 @@ c-version-name: ethtool-genl-version
       -
         name: input-xfrm
         type: u32
+        enum: input-xfrm
       -
         name: start-context
         type: u32
diff --git a/tools/testing/selftests/drivers/net/hw/rss_input_xfrm.py b/tools/testing/selftests/drivers/net/hw/rss_input_xfrm.py
index 648ff50bc1c3..6e90fb290564 100755
--- a/tools/testing/selftests/drivers/net/hw/rss_input_xfrm.py
+++ b/tools/testing/selftests/drivers/net/hw/rss_input_xfrm.py
@@ -37,11 +37,11 @@ from lib.py import rand_port
     if not hasattr(socket, "SO_INCOMING_CPU"):
         raise KsftSkipEx("socket.SO_INCOMING_CPU was added in Python 3.11")
 
-    input_xfrm = cfg.ethnl.rss_get(
-        {'header': {'dev-name': cfg.ifname}}).get('input-xfrm')
+    rss = cfg.ethnl.rss_get({'header': {'dev-name': cfg.ifname}})
+    input_xfrm = set(filter(lambda x: 'sym' in x, rss.get('input-xfrm', {})))
 
     # Check for symmetric xor/or-xor
-    if not input_xfrm or (input_xfrm != 1 and input_xfrm != 2):
+    if not input_xfrm:
         raise KsftSkipEx("Symmetric RSS hash not requested")
 
     cpus = set()
-- 
2.50.1