Re: [dpdk-dev] [RFC] doc: announce max Rx packet len field deprecation

[Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>]

On 10/21/20 1:18 PM, Ananyev, Konstantin wrote:
>
>
>> Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
>> ---
>> Cc: Thomas Monjalon <thomas@monjalon.net>
>> Cc: Andrew Rybchenko <arybchenko@solarflare.com>
>> Cc: Konstantin Ananyev <konstantin.ananyev@intel.com>
>> Cc: Matan Azrad <matan@nvidia.com>
>> Cc: Olivier Matz <olivier.matz@6wind.com>
>> Cc: Jerin Jacob <jerinj@marvell.com>
>> ---
>>   doc/guides/rel_notes/deprecation.rst | 25 +++++++++++++++++++++++++
>>   1 file changed, 25 insertions(+)
>>
>> diff --git a/doc/guides/rel_notes/deprecation.rst b/doc/guides/rel_notes/deprecation.rst
>> index 8ceb385141..d4a31392d3 100644
>> --- a/doc/guides/rel_notes/deprecation.rst
>> +++ b/doc/guides/rel_notes/deprecation.rst
>> @@ -149,6 +149,31 @@ Deprecation Notices
>>     will be limited to maximum 256 queues.
>>     Also compile time flag ``RTE_ETHDEV_QUEUE_STAT_CNTRS`` will be removed.
>>
>> +* ethdev: In ``struct rte_eth_rxmode``, ``uint32_t max_rx_pkt_len`` will be
>> +  replaced by a new ``uint32_t mtu`` in v21.11.
> Probably no point to keep mtu value in rte_eth_rxmode.
> Better to move it to rte_eth_conf.
> Apart from that: +1 for this change.
> Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>

Do we really need the field in either rte_eth_rxmode or rte_eth_conf?
What's the point of duplication? We have dedicated API to get/set
which could be called in stopped state, set value saved in
data->mtu and used by the driver at start up and Rx queues setup
(to check scatter vs data room in mbuf consistency).

>> +  The new ``mtu`` field will be used to configure the initial device MTU via
>> +  ``rte_eth_dev_configure()`` API.
>> +  Later MTU can be changed by ``rte_eth_dev_set_mtu()`` API as done now.
>> +  The existing ``(struct rte_eth_dev)->data->mtu`` variable will be used to store
>> +  the configured ``mtu`` value,
>> +  and this new ``(struct rte_eth_dev)->data->dev_conf.rxmode.mtu`` variable will
>> +  be used to store the user configuration request.
>> +  Unlike ``max_rx_pkt_len``, which was valid only when ``JUMBO_FRAME`` enabled,
>> +  ``mtu`` field will be always valid.
>> +  When ``mtu`` config is not provided by the application, default ``RTE_ETHER_MTU``
>> +  value will be used.
>> +  Driver is responsible from updating ``(struct rte_eth_dev)->data->mtu`` after MTU
>> +  set successfully, either by ``rte_eth_dev_configure()`` or ``rte_eth_dev_set_mtu()``.
>> +
>> +  Application may need to configure device for a specific Rx packet size, like for
>> +  cases ``DEV_RX_OFFLOAD_SCATTER`` is not supported and device received packet size
>> +  can't be bigger than Rx buffer size.
>> +  To cover these cases application needs to know the device packet overhead to be
>> +  able to calculate the ``mtu`` corresponding to a Rx buffer size, for this
>> +  ``(struct rte_eth_dev_info).max_rx_pktlen`` will be kept,
>> +  the device packet overhead can be calculated as:
>> +  ``(struct rte_eth_dev_info).max_rx_pktlen - (struct rte_eth_dev_info).max_mtu``
>> +
>>   * cryptodev: support for using IV with all sizes is added, J0 still can
>>     be used but only when IV length in following structs ``rte_crypto_auth_xform``,
>>     ``rte_crypto_aead_xform`` is set to zero. When IV length is greater or equal
>> --
>> 2.26.2