Re: [dpdk-dev] [PATCH] ethdev: add new offload flag to keep CRC

[Andrew Rybchenko <arybchenko@solarflare.com>]

On 06/20/2018 08:24 PM, Ferruh Yigit wrote:
> On 6/20/2018 8:42 AM, Andrew Rybchenko wrote:
>> On 06/19/2018 09:02 PM, Ferruh Yigit wrote:
>>> DEV_RX_OFFLOAD_KEEP_CRC offload flag added. PMDs that supports keeping
>>> CRC should advertise this offload capability.
>>>
>>> DEV_RX_OFFLOAD_CRC_STRIP flag will remain one more release
>>> default behavior in PMDs are to keep the CRC until this flag removed
>>>
>>> Until DEV_RX_OFFLOAD_CRC_STRIP flag is removed:
>>> - Setting both KEEP_CRC & CRC_STRIP is INVALID
>>> - Setting only CRC_STRIP PMD should strip the CRC
>>> - Setting only KEEP_CRC PMD should keep the CRC
>>> - Not setting both PMD should keep the CRC
>>>
>>> A helper function rte_eth_dev_is_keep_crc() has been added to be able to
>>> change the no flag behavior with minimal changes in PMDs.
>>>
>>> The PMDs that doesn't report the DEV_RX_OFFLOAD_KEEP_CRC offload can
>>> remove rte_eth_dev_is_keep_crc() checks next release, related code
>>> commented to help the maintenance task.
>>>
>>> And DEV_RX_OFFLOAD_CRC_STRIP has been added to virtual drivers since
>>> they don't use CRC at all, when an application requires this offload
>>> virtual PMDs should not return error.
>>>
>>> Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
>>> ---
>> <...>
>>
>>> diff --git a/lib/librte_ethdev/rte_ethdev_driver.h b/lib/librte_ethdev/rte_ethdev_driver.h
>>> index c9c825e3f..09a42f8c2 100644
>>> --- a/lib/librte_ethdev/rte_ethdev_driver.h
>>> +++ b/lib/librte_ethdev/rte_ethdev_driver.h
>>> @@ -325,6 +325,26 @@ typedef int (*ethdev_uninit_t)(struct rte_eth_dev *ethdev);
>>>   int __rte_experimental
>>>   rte_eth_dev_destroy(struct rte_eth_dev *ethdev, ethdev_uninit_t ethdev_uninit);
>>>   
>>> +/**
>>> + * PMD helper function to check if keeping CRC is requested
>>> + *
>>> + * @param rx_offloads
>>> + *   offloads variable
>>> + *
>>> + * @return
>>> + *   Return positive if keeping CRC is requested,
>>> + *   zero if stripping CRC is requested
>>> + */
>>> +static inline int
>>> +rte_eth_dev_is_keep_crc(uint64_t rx_offloads)
>>> +{
>>> +	if (rx_offloads & DEV_RX_OFFLOAD_CRC_STRIP)
>>> +		return 0;
>>> +
>>> +	/* no KEEP_CRC or CRC_STRIP offload flags means keep CRC */
>>> +	return 1;
>>> +}
>>> +
>>>   #ifdef __cplusplus
>>>   }
>>>   #endif
>> A couple of control questions about the function:
>>   - shouldn't __rte_experimental be used?
> This is an internal function, not API, so I think doesn't require to be
> experimental.

Just to make my thoughts clear: description does not say that it is an 
internal.
So, nothing prevents external entities to use it. Changes will be API 
breakage.

>>   - if the function remains in the future, it will be a bit asymmetric vs other
>>     offload flags. Right now it is clear why the function is introduced, but
>>     it is the question if the function should remain or go away in the future
>>     (as far as I know no other offload flag has similar function to check).
> No other offloads don't have similar functions, this is kind special.
>
> There will be more changes related CRC next release, CRC_STRIP will be removed
> and no flag will mean strip CRC. So the conditions to is_keep_crc will be changed.
> This function is to manage this change easier, localize the information in to
> single function to make it easy to update later.

It is perfectly clear why it is required right now and introduced (as I said
from the very beginning).
Yes, it is will be the history which explains why it is so, but if we make
a step forward and discard the history it will look asymmetric -
it will be a function which checks single bit. It is really minor and
100% up to you.

Many thanks for reply.