ethtool: netlink: add ETHTOOL_MSG_MSE_GET and wire up PHY MSE access

Introduce the userspace entry point for PHY MSE diagnostics via
ethtool netlink. This exposes the core API added previously and
returns both capability information and one or more snapshots.

Userspace sends ETHTOOL_MSG_MSE_GET. The reply carries:
- ETHTOOL_A_MSE_CAPABILITIES: scale limits and timing information
- ETHTOOL_A_MSE_CHANNEL_* nests: one or more snapshots (per-channel
  if available, otherwise WORST, otherwise LINK)

Link down returns -ENETDOWN.

Changes:
  - YAML: add attribute sets (mse, mse-capabilities, mse-snapshot)
    and the mse-get operation
  - UAPI (generated): add ETHTOOL_A_MSE_* enums and message IDs,
    ETHTOOL_MSG_MSE_GET/REPLY
  - ethtool core: add net/ethtool/mse.c implementing the request,
    register genl op, and hook into ethnl dispatch
  - docs: document MSE_GET in ethtool-netlink.rst

The include/uapi/linux/ethtool_netlink_generated.h is generated
from Documentation/netlink/specs/ethtool.yaml.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://patch.msgid.link/20251027122801.982364-3-o.rempel@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 64 insertions, 0 deletions

diff --git a/Documentation/networking/ethtool-netlink.rst b/Documentation/networking/ethtool-netlink.rst
index b270886c5f5d..af56c304cef4 100644
--- a/Documentation/networking/ethtool-netlink.rst
+++ b/Documentation/networking/ethtool-netlink.rst
@@ -242,6 +242,7 @@ Userspace to kernel:
   ``ETHTOOL_MSG_RSS_SET``               set RSS settings
   ``ETHTOOL_MSG_RSS_CREATE_ACT``        create an additional RSS context
   ``ETHTOOL_MSG_RSS_DELETE_ACT``        delete an additional RSS context
+  ``ETHTOOL_MSG_MSE_GET``               get MSE diagnostic data
   ===================================== =================================
 
 Kernel to userspace:
@@ -299,6 +300,7 @@ Kernel to userspace:
   ``ETHTOOL_MSG_RSS_CREATE_ACT_REPLY``     create an additional RSS context
   ``ETHTOOL_MSG_RSS_CREATE_NTF``           additional RSS context created
   ``ETHTOOL_MSG_RSS_DELETE_NTF``           additional RSS context deleted
+  ``ETHTOOL_MSG_MSE_GET_REPLY``            MSE diagnostic data
   ======================================== =================================
 
 ``GET`` requests are sent by userspace applications to retrieve device
@@ -2458,6 +2460,68 @@ Kernel response contents:
 
 For a description of each attribute, see ``TSCONFIG_GET``.
 
+MSE_GET
+=======
+
+Retrieves detailed Mean Square Error (MSE) diagnostic information from the PHY.
+
+Request Contents:
+
+  ====================================  ======  ============================
+  ``ETHTOOL_A_MSE_HEADER``              nested  request header
+  ====================================  ======  ============================
+
+Kernel Response Contents:
+
+  ====================================  ======  ================================
+  ``ETHTOOL_A_MSE_HEADER``              nested  reply header
+  ``ETHTOOL_A_MSE_CAPABILITIES``        nested  capability/scale info for MSE
+                                                measurements
+  ``ETHTOOL_A_MSE_CHANNEL_A``           nested  snapshot for Channel A
+  ``ETHTOOL_A_MSE_CHANNEL_B``           nested  snapshot for Channel B
+  ``ETHTOOL_A_MSE_CHANNEL_C``           nested  snapshot for Channel C
+  ``ETHTOOL_A_MSE_CHANNEL_D``           nested  snapshot for Channel D
+  ``ETHTOOL_A_MSE_WORST_CHANNEL``       nested  snapshot for worst channel
+  ``ETHTOOL_A_MSE_LINK``                nested  snapshot for link-wide aggregate
+  ====================================  ======  ================================
+
+MSE Capabilities
+----------------
+
+This nested attribute reports the capability / scaling properties used to
+interpret snapshot values.
+
+  ============================================== ======  =========================
+  ``ETHTOOL_A_MSE_CAPABILITIES_MAX_AVERAGE_MSE`` uint    max avg_mse scale
+  ``ETHTOOL_A_MSE_CAPABILITIES_MAX_PEAK_MSE``    uint    max peak_mse scale
+  ``ETHTOOL_A_MSE_CAPABILITIES_REFRESH_RATE_PS`` uint    sample rate (picoseconds)
+  ``ETHTOOL_A_MSE_CAPABILITIES_NUM_SYMBOLS``     uint    symbols per HW sample
+  ============================================== ======  =========================
+
+The max-average/peak fields are included only if the corresponding metric
+is supported by the PHY. Their absence indicates that the metric is not
+available.
+
+See ``struct phy_mse_capability`` kernel documentation in
+``include/linux/phy.h``.
+
+MSE Snapshot
+------------
+
+Each per-channel nest contains an atomic snapshot of MSE values for that
+selector (channel A/B/C/D, worst channel, or link).
+
+  ==========================================  ======  ===================
+  ``ETHTOOL_A_MSE_SNAPSHOT_AVERAGE_MSE``      uint    average MSE value
+  ``ETHTOOL_A_MSE_SNAPSHOT_PEAK_MSE``         uint    current peak MSE
+  ``ETHTOOL_A_MSE_SNAPSHOT_WORST_PEAK_MSE``   uint    worst-case peak MSE
+  ==========================================  ======  ===================
+
+Within each channel nest, only the metrics supported by the PHY will be present.
+
+See ``struct phy_mse_snapshot`` kernel documentation in
+``include/linux/phy.h``.
+
 Request translation
 ===================