net: ethtool: Allow passing a phy index for some commands

Some netlink commands are target towards ethernet PHYs, to control some
of their features. As there's several such commands, add the ability to
pass a PHY index in the ethnl request, which will populate the generic
ethnl_req_info with the passed phy_index.

Add a helper that netlink command handlers need to use to grab the
targeted PHY from the req_info. This helper needs to hold rtnl_lock()
while interacting with the PHY, as it may be removed at any point.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Tested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 0 deletions

diff --git a/Documentation/networking/ethtool-netlink.rst b/Documentation/networking/ethtool-netlink.rst
index 3f6c6880e7c4..2d14b8551348 100644
--- a/Documentation/networking/ethtool-netlink.rst
+++ b/Documentation/networking/ethtool-netlink.rst
@@ -57,6 +57,7 @@ Structure of this header is
   ``ETHTOOL_A_HEADER_DEV_INDEX``  u32     device ifindex
   ``ETHTOOL_A_HEADER_DEV_NAME``   string  device name
   ``ETHTOOL_A_HEADER_FLAGS``      u32     flags common for all requests
+  ``ETHTOOL_A_HEADER_PHY_INDEX``  u32     phy device index
   ==============================  ======  =============================
 
 ``ETHTOOL_A_HEADER_DEV_INDEX`` and ``ETHTOOL_A_HEADER_DEV_NAME`` identify the
@@ -81,6 +82,12 @@ the behaviour is backward compatible, i.e. requests from old clients not aware
 of the flag should be interpreted the way the client expects. A client must
 not set flags it does not understand.
 
+``ETHTOOL_A_HEADER_PHY_INDEX`` identifies the Ethernet PHY the message relates to.
+As there are numerous commands that are related to PHY configuration, and because
+there may be more than one PHY on the link, the PHY index can be passed in the
+request for the commands that needs it. It is, however, not mandatory, and if it
+is not passed for commands that target a PHY, the net_device.phydev pointer
+is used.
 
 Bit sets
 ========