ethtool: doc: clarify what drivers can implement in their get_drvinfo()

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.

In struct ethtool_ops doc from linux/ethtool: rephrase field
get_drvinfo() doc to discourage developers from implementing this
callback.

In struct ethtool_drvinfo doc from uapi/linux/ethtool.h: remove the
paragraph mentioning what drivers should do. Rationale: no need to
repeat what is already written in struct ethtool_ops doc. But add a
note that .fw_version and .erom_version are driver defined.

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 6a7e25c7 ("net/core: Replace driver version to be
    kernel version")
Link: https://git.kernel.org/torvalds/linux/c/6a7e25c7fb48

[2] commit edaf5df2 ("ethtool: ethtool_get_drvinfo: populate
    drvinfo fields even if callback exits")
Link: https://git.kernel.org/netdev/net-next/c/edaf5df22cb8Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Link: https://lore.kernel.org/r/20221116171828.4093-1-mailhol.vincent@wanadoo.frSigned-off-by: Jakub Kicinski <kuba@kernel.org>

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,
 };
 

include/linux/ethtool.h

@@ -473,10 +473,10 @@ struct ethtool_module_power_mode_params {
  *	parameter.
  * @supported_coalesce_params: supported types of interrupt coalescing.
  * @supported_ring_params: supported ring params.
- * @get_drvinfo: Report driver/device information.  Should only set the
- *	@driver, @version, @fw_version and @bus_info fields.  If not
- *	implemented, the @driver and @bus_info fields will be filled in
- *	according to the netdev's parent device.
+ * @get_drvinfo: Report driver/device information. Modern drivers no
+ *	longer have to implement this callback. Most fields are
+ *	correctly filled in by the core using system information, or
+ *	populated using other driver operations.
  * @get_regs_len: Get buffer length required for @get_regs
  * @get_regs: Get device registers
  * @get_wol: Report whether Wake-on-Lan is enabled

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.
@@ -179,10 +181,6 @@ 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.
  */
 struct ethtool_drvinfo {
 	__u32	cmd;