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 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>
Link: https://lore.kernel.org/r/20221116171828.4093-1-mailhol.vincent@wanadoo.fr
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 4 insertions, 4 deletions

diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
index 5c51c7fda32a..9e0a76fc7de9 100644
--- a/include/linux/ethtool.h
+++ b/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