devlink: Introduce switchdev_inactive eswitch mode

Adds DEVLINK_ESWITCH_MODE_SWITCHDEV_INACTIVE attribute to UAPI and
documentation.

Before having traffic flow through an eswitch, a user may want to have the
ability to block traffic towards the FDB until FDB is fully programmed and
the user is ready to send traffic to it. For example: when two eswitches
are present for vports in a multi-PF setup, one eswitch may take over the
traffic from the other when the user chooses.
Before this take over, a user may want to first program the inactive
eswitch and then once ready redirect traffic to this new eswitch.

switchdev modes transition semantics:

legacy->switchdev_inactive: Create switchdev mode normally, traffic not
  allowed to flow yet.

switchdev_inactive->switchdev: Enable traffic to flow.

switchdev->switchdev_inactive: Block traffic on the FDB, FDB and
  representros state and content is preserved.

When eswitch is configured to this mode, traffic is ignored/dropped on
this eswitch FDB, while current configuration is kept, e.g FDB rules and
netdev representros are kept available, FDB programming is allowed.

Example:
 # start inactive switchdev
devlink dev eswitch set pci/0000:08:00.1 mode switchdev_inactive
 # setup TC rules, representors etc ..
 # activate
devlink dev eswitch set pci/0000:08:00.1 mode switchdev

Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://patch.msgid.link/20251108070404.1551708-2-saeed@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Documentation/netlink/specs/devlink.yaml

@@ -99,6 +99,8 @@ definitions:
         name: legacy
       -
         name: switchdev
+      -
+        name: switchdev-inactive
   -
     type: enum
     name: eswitch-inline-mode

Documentation/networking/devlink/devlink-eswitch-attr.rst

@@ -39,6 +39,10 @@ The following is a list of E-Switch attributes.
          rules.
        * ``switchdev`` allows for more advanced offloading capabilities of
          the E-Switch to hardware.
+       * ``switchdev_inactive`` switchdev mode but starts inactive, doesn't allow traffic
+         until explicitly activated. This mode is useful for orchestrators that
+         want to prepare the device in switchdev mode but only activate it when
+         all configurations are done.
    * - ``inline-mode``
      - enum
      - Some HWs need the VF driver to put part of the packet
@@ -74,3 +78,12 @@ Example Usage
 
     # enable encap-mode with legacy mode
     $ devlink dev eswitch set pci/0000:08:00.0 mode legacy inline-mode none encap-mode basic
+
+    # start switchdev mode in inactive state
+    $ devlink dev eswitch set pci/0000:08:00.0 mode switchdev_inactive
+
+    # setup switchdev configurations, representors, FDB entries, etc..
+    ...
+
+    # activate switchdev mode to allow traffic
+    $ devlink dev eswitch set pci/0000:08:00.0 mode switchdev

include/uapi/linux/devlink.h

@@ -181,6 +181,7 @@ enum devlink_sb_threshold_type {
 enum devlink_eswitch_mode {
 	DEVLINK_ESWITCH_MODE_LEGACY,
 	DEVLINK_ESWITCH_MODE_SWITCHDEV,
+	DEVLINK_ESWITCH_MODE_SWITCHDEV_INACTIVE,
 };
 
 enum devlink_eswitch_inline_mode {

net/devlink/netlink_gen.c

@@ -229,7 +229,7 @@ static const struct nla_policy devlink_eswitch_get_nl_policy[DEVLINK_ATTR_DEV_NA
 static const struct nla_policy devlink_eswitch_set_nl_policy[DEVLINK_ATTR_ESWITCH_ENCAP_MODE + 1] = {
 	[DEVLINK_ATTR_BUS_NAME] = { .type = NLA_NUL_STRING, },
 	[DEVLINK_ATTR_DEV_NAME] = { .type = NLA_NUL_STRING, },
-	[DEVLINK_ATTR_ESWITCH_MODE] = NLA_POLICY_MAX(NLA_U16, 1),
+	[DEVLINK_ATTR_ESWITCH_MODE] = NLA_POLICY_MAX(NLA_U16, 2),
 	[DEVLINK_ATTR_ESWITCH_INLINE_MODE] = NLA_POLICY_MAX(NLA_U8, 3),
 	[DEVLINK_ATTR_ESWITCH_ENCAP_MODE] = NLA_POLICY_MAX(NLA_U8, 1),
 };