[PATCH net-next v4] ethtool: doc: clarify what drivers can implement in their get_drvinfo()

[PATCH net-next v4] ethtool: doc: clarify what drivers can implement in their get_drvinfo()

[Vincent Mailhol]

Many of the drivers which implement ethtool_ops::get_drvinfo() will
prints the .driver, .version or .bus_info of struct ethtool_drvinfo.
To have a glance of current state, do:

  $ git grep -W "get_drvinfo(struct"

Printing in those three fields is useless because:

  - since [1], the driver version should be the kernel version (at
    least for upstream drivers). Arguably, out of tree drivers might
    still want to set a custom version, but out of tree is not our
    focus.

  - since [2], the core is able to provide default values for .driver
    and .bus_info.

In summary, drivers may provide .fw_version and .erom_version, the
rest is expected to be done by the core. Update the doc to reflect the
facts and discourage developers from implementing the get_drvinfo()
callback.

Also update the dummy driver and simply remove the callback in order
not to confuse the newcomers: most of the drivers will not need this
callback function any more.

[1] commit 6a7e25c7fb48 ("net/core: Replace driver version to be
    kernel version")
Link: https://git.kernel.org/torvalds/linux/c/6a7e25c7fb48

[2] commit edaf5df22cb8 ("ethtool: ethtool_get_drvinfo: populate
    drvinfo fields even if callback exits")
Link: https://git.kernel.org/netdev/net-next/c/edaf5df22cb8

Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
---
* Changelog *

v3 -> v4:

  * rephrasing of the documentation according to Jakub's comments.

v2 -> v3:

  * add Reviewed-by: Leon Romanovsky <leonro@nvidia.com> tag.
    * use shorter links.

v1 -> v2:

  * forgot the net-next prefix in the patch subject... Sorry for the
      noise.
---
 drivers/net/dummy.c          |  7 -------
 include/uapi/linux/ethtool.h | 12 +++++++-----
 2 files changed, 7 insertions(+), 12 deletions(-)

diff --git a/drivers/net/dummy.c b/drivers/net/dummy.c
index aa0fc00faecb..c4b1b0aa438a 100644
--- a/drivers/net/dummy.c
+++ b/drivers/net/dummy.c
@@ -99,14 +99,7 @@ static const struct net_device_ops dummy_netdev_ops = {
 	.ndo_change_carrier	= dummy_change_carrier,
 };
 
-static void dummy_get_drvinfo(struct net_device *dev,
-			      struct ethtool_drvinfo *info)
-{
-	strscpy(info->driver, DRV_NAME, sizeof(info->driver));
-}
-
 static const struct ethtool_ops dummy_ethtool_ops = {
-	.get_drvinfo            = dummy_get_drvinfo,
 	.get_ts_info		= ethtool_op_get_ts_info,
 };
 
diff --git a/include/uapi/linux/ethtool.h b/include/uapi/linux/ethtool.h
index dc2aa3d75b39..e801bd4bd6c7 100644
--- a/include/uapi/linux/ethtool.h
+++ b/include/uapi/linux/ethtool.h
@@ -159,8 +159,10 @@ static inline __u32 ethtool_cmd_speed(const struct ethtool_cmd *ep)
  *	in its bus driver structure (e.g. pci_driver::name).  Must
  *	not be an empty string.
  * @version: Driver version string; may be an empty string
- * @fw_version: Firmware version string; may be an empty string
- * @erom_version: Expansion ROM version string; may be an empty string
+ * @fw_version: Firmware version string; driver defined; may be an
+ *	empty string
+ * @erom_version: Expansion ROM version string; driver defined; may be
+ *	an empty string
  * @bus_info: Device bus address.  This should match the dev_name()
  *	string for the underlying bus device, if there is one.  May be
  *	an empty string.
@@ -180,9 +182,9 @@ static inline __u32 ethtool_cmd_speed(const struct ethtool_cmd *ep)
  * Users can use the %ETHTOOL_GSSET_INFO command to get the number of
  * strings in any string set (from Linux 2.6.34).
  *
- * Drivers should set at most @driver, @version, @fw_version and
- * @bus_info in their get_drvinfo() implementation.  The ethtool
- * core fills in the other fields using other driver operations.
+ * Modern drivers no longer have to implement the get_drvinfo()
+ * callback. Most fields are correctly filled in by the core using
+ * system information, or populated using other driver operations.
  */
 struct ethtool_drvinfo {
 	__u32	cmd;
-- 
2.25.1