[RFC v2 1/3] ethdev: add frequency adjustment API

[Thomas Monjalon]

Hello,

03/04/2023 11:22, Simei Su:
> This patch introduces a new timesync API "rte_eth_timesync_adjust_freq"
> which enables frequency adjustment during PTP timesync.

You should explain how it compares with existing functions
like rte_eth_timesync_adjust_time().

[...]
>  /**
> + * Adjust the clock increment rate on an Ethernet device.
> + *
> + * This is usually used in conjunction with other Ethdev timesync functions to
> + * synchronize the device time using the IEEE1588/802.1AS protocol.

All timesync functions have this sentence,
but it does not help to understand how to combine them.

> + *
> + * @param port_id
> + *  The port identifier of the Ethernet device.
> + * @param ppm
> + *  Parts per million with 16-bit fractional field

Sorry I don't understand what this parameter is about.
Probably because I'm not an expert of IEEE1588/802.1AS protocol.
Please make it possible to understand for basic users.

> + *
> + * @return
> + *   - 0: Success.
> + *   - -ENODEV: The port ID is invalid.
> + *   - -EIO: if device is removed.
> + *   - -ENOTSUP: The function is not supported by the Ethernet driver.
> + */
> +int rte_eth_timesync_adjust_freq(uint16_t port_id, int64_t ppm);

In general, I think there is an effort to provide in order to make
the timesync API better understandable.
Example of something to explain: how Rx and Tx timestamps of a port
are differents? Is it different of rte_eth_timesync_read_time()?

The function rte_eth_read_clock() was provided with a better explanation.

Please make improvements in API documentation as part of this API,
I don't want to get more functions without improving explanation
of older functions.
Thank you