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

[Andrew Rybchenko <arybchenko@solarflare.com>]

On 20.06.2018 21:12, Ferruh Yigit wrote:
> On 6/20/2018 6:39 PM, Andrew Rybchenko wrote:
>> 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.
> rte_ethdev_driver.h is not public header, it is just for PMDs.

I see. So, it will not be a problem to remove it. OK.

>>>>   - 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.
> I see, right it will be just a wrapper to bit check. In this patch it helps to
> revert to logic, from strip_crc to keep_crc. In next release I am OK to remove
> function and return back to bit check in PMDs, will this be more reasonable?

Just for consistency I'd say yes.