A if `netdev_driver_t::confirm_send()` is provided, it provides the
new netdev API. However, detecting the API at runtime and handling
both API styles comes at a cost. This can be optimized in case only
new or only old style netdevs are in use.
To do so, this adds the pseudo modules `netdev_legacy_api` and
`netdev_new_api`. As right now no netdev actually implements the new
API, all netdevs pull in `netdev_legacy_api`. If `netdev_legacy_api` is
in used but `netdev_new_api` is not, we can safely assume at compile
time that only legacy netdevs are in use. Similar, if only
`netdev_new_api` is used, only support for the new API is needed. Only
when both are in use, run time checks are needed.
This provides two helper function to check for a netif if the
corresponding netdev implements the old or the new API. (With one
being the inverse of the other.) They are suitable for constant folding
when only new or only legacy devices are in use. Consequently, dead
branches should be eliminated by the optimizer.
A single character type resulted in way fewer TX descriptors being
available than allocated. Not only resulted this in wasting memory,
but also when more iolist chunks than descriptors are send, the
```C
assert(iolist_count(iolist) <= ETH_TX_DESCRIPTOR_COUNT);
```
does not trigger. As a result, old TX descriptors are being overwritten
in this case.
An network devices that supports netdev_driver_t::get(NETOPT_LINK, ...)
also has to emit NETDEV_EVENT_LINK_UP and NETDEV_EVENT_LINK_DOWN with
lwip for IPv6 duplicate address detection to work. The background is
that the STM32 Ethernet MAC requires a periodic timer to poll for the
state to emit these events. For this reason, `stm32_eth_link_up` was
introduced to allow applications to select if they need these events.
With this dependency in place, IPv6 addresses won't get stuck in a
tentative state any more.
This introduces KCONFIG_BOARD_CONFIG and KCONFIG_CPU_CONFIG variable for
boards and CPUs (including common directories) to add default
configuration files to be merged. The current approach, as it uses
Makefile.features, would include boards first, not allowing them to
override CPU configurations.
