Re: [RFC PATCH net-next v3 1/6] ethtool: Add ability to control transceiver modules' power mode

quoted

quoted

+ * @mode_valid: Indicates the validity of the @mode field. Should be set by
+ * device drivers on get operations when a module is plugged-in.  

Should we make a firm decision on whether we want to use these kind of
valid bits or choose invalid defaults? As you may guess my preference
is the latter since that's what I usually do, that way drivers don't
have to write two fields.

Actually I think this may be the first "valid" in ethtool, I thought we
already had one but I don't see it now..  

I was thinking about this as well, but I wasn't sure if it's valid to
adjust uAPI values in order to make in-kernel APIs simpler. I did see it
in some other places, but wasn't sure if it's a pattern that should be
copied.

Do you mean something like this?

diff --git a/include/uapi/linux/ethtool.h b/include/uapi/linux/ethtool.h
index 7d453f0e993b..d61049091538 100644
--- a/include/uapi/linux/ethtool.h
+++ b/include/uapi/linux/ethtool.h

@@ -732,7 +732,7 @@ enum ethtool_module_power_mode_policy {
  * @ETHTOOL_MODULE_POWER_MODE_HIGH: Module is in high power mode.
  */
 enum ethtool_module_power_mode {
-       ETHTOOL_MODULE_POWER_MODE_LOW,
+       ETHTOOL_MODULE_POWER_MODE_LOW = 1,
        ETHTOOL_MODULE_POWER_MODE_HIGH,
 };

I prefer this over memsetting a struct to 0xff.

If the above is fine, I can make the following patch:

diff --git a/Documentation/networking/ethtool-netlink.rst b/Documentation/networking/ethtool-netlink.rst
index c258b3f30a2e..d304df39ee5c 100644
--- a/Documentation/networking/ethtool-netlink.rst
+++ b/Documentation/networking/ethtool-netlink.rst

@@ -41,6 +41,11 @@ In the message structure descriptions below, if an attribute name is suffixed
 with "+", parent nest can contain multiple attributes of the same type. This
 implements an array of entries.
 
+Attributes that need to be filled-in by device drivers and that are dumped to
+user space based on whether they are valid or not should not use zero as a
+valid value. For example, ``ETHTOOL_A_MODULE_POWER_MODE``. This avoids the need
+to explicitly signal the validity of the attribute in the device driver API.
+