Re: [dpdk-dev] [PATCH v2 2/2] ethdev: add new offload flag to keep CRC

[Shahaf Shuler <shahafs@mellanox.com>]

Thursday, March 29, 2018 10:43 AM, Thomas Monjalon:
> 29/03/2018 07:38, Shahaf Shuler:
> > Wednesday, March 21, 2018 9:48 PM, Ferruh Yigit:
> > > DEV_RX_OFFLOAD_KEEP_CRC offload flag added.
> > >
> > > DEV_RX_OFFLOAD_CRC_STRIP flag will remain one more release but
> > > default behavior in PMDs is to strip the CRC independent from this flag.
> > >
> > > 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 strip the CRC
> >
> > We cannot have such default behavior, it may break existing applications.
> >
> > The API of ethdev offloads says (even though it is not well documented) :
> DEV_RX_OFFLOAD_CRC_STRIP (emphasis the STRIP).
> > meaning, if set -> STRIP, if not set -> don't strip.  I am aware to at least one
> application which wants to have the CRC, and for that purpose it naturally
> don't set the offload flag.
> >
> > The fact some PMDs lack the ability to toggle the CRC stripping should be
> exposed in the "limitations" section of their related guide.
> >
> > Up to here, this is the behavior as defined by the API.
> >
> > Now, we want to change it, and I think it makes sense. However I think we
> should take similar approach to what we did with the ethdev offloads API:
> > 1. at first stage a new offload flag is exposed DEV_RX_OFFLOAD_KEEP_CRC
> and implemented on the PMDs.
> 
> This is what is proposed above, except that we change the default
> behaviour.
> If we introduce a new flag which is the contrary of the old one, we need to
> choose which one is the default, so which one has no effect.

The default behavior should remain as long as we don't deprecate the DEV_RX_OFFLOAD_CRC_STRIP flag.

Logic should be :
Until DEV_RX_OFFLOAD_CRC_STRIP flag is removed:
 - Setting both KEEP_CRC & CRC_STRIP is INVALID - enforced by ethdev. 
 - Setting only CRC_STRIP PMD should strip the CRC
 - Setting only KEEP_CRC PMD should keep the CRC
 - Not setting both PMD should *not* strip the CRC 

> 
> > 2. there is a conversion function on ethdev. Which for example converts
> ~DEV_RX_OFFLOAD_CRC_STRIP -> DEV_RX_OFFLOAD_KEEP_CRC for the
> PMDs.
> > 3. deprecation of DEV_RX_OFFLOAD_CRC_STRIP for applications and
> remove of the conversion functions.
> 
> 
>