Re: [PATCH v2 1/2] build: clarify configuration without IOVA field in mbuf

[Bruce Richardson <bruce.richardson@intel.com>]

On Thu, Mar 09, 2023 at 01:12:51PM +0100, Thomas Monjalon wrote:
> 09/03/2023 12:23, fengchengwen:
> > On 2023/3/9 15:29, Thomas Monjalon wrote:
> > > 09/03/2023 02:43, fengchengwen:
> > >> On 2023/3/7 0:13, Thomas Monjalon wrote:
> > >>> --- a/doc/guides/rel_notes/release_22_11.rst
> > >>> +++ b/doc/guides/rel_notes/release_22_11.rst
> > >>> @@ -504,7 +504,7 @@ ABI Changes
> > >>>    ``rte-worker-<lcore_id>`` so that DPDK can accommodate lcores higher than 99.
> > >>>  
> > >>>  * mbuf: Replaced ``buf_iova`` field with ``next`` field and added a new field
> > >>> -  ``dynfield2`` at its place in second cacheline if ``RTE_IOVA_AS_PA`` is 0.
> > >>> +  ``dynfield2`` at its place in second cacheline if ``RTE_IOVA_IN_MBUF`` is 0.
> > >>
> > >> Should add to release 23.03 rst.
> > > 
> > > Yes we could add a note in API changes.
> > > 
> > >> The original 22.11 still have RTE_IOVA_AS_PA definition.
> > > 
> > > Yes it was not a good idea to rename in the release notes.
> > > 
> > >>> -if dpdk_conf.get('RTE_IOVA_AS_PA') == 0
> > >>> -    build = false
> > >>> -    reason = 'driver does not support disabling IOVA as PA mode'
> > >>> +if not get_option('enable_iova_as_pa')
> > >>>      subdir_done()
> > >>>  endif
> > >>
> > >> Suggest keep original, and replace RTE_IOVA_AS_PA with RTE_IOVA_IN_MBUF:
> > >> if dpdk_conf.get('RTE_IOVA_IN_MBUF') == 0
> > >>      subdir_done()
> > >> endif
> > > 
> > > Why testing the C macro in Meson?
> > > It looks simpler to check the Meson option in Meson.
> > 
> > The macro was create in meson.build: config/meson.build:319:dpdk_conf.set10('RTE_IOVA_AS_PA', get_option('enable_iova_as_pa'))
> > It can be regarded as alias of enable_iova_as_pa.
> 
> It is not strictly an alias, because it can be overriden via CFLAGS.
> 
> > This commit was mainly used to improve comprehensibility. so we should limit the 'enable_iova_as_pa' usage scope.
> > and the 'if dpdk_conf.get('RTE_IOVA_IN_MBUF') == 0' is more comprehensibility than 'if not get_option('enable_iova_as_pa')'
> 
> To me, using Meson option in Meson files is more obvious.
> 
> Bruce, what do you think?
> 

I'm not sure it matters much! However, I think of the two, using the
reference to IOVA_IN_MBUF is clearer. It also allows the same terminology
to be used in meson and C files. If we don't want to do a dpdk_conf lookup,
we can always assign the option to a meson variable called iova_in_mbuf.

/Bruce