Re: [dpdk-dev] [PATCH v5 1/1] vfio: modify spapr iommu support to use static window sizing

[Thomas Monjalon <thomas@monjalon.net>]

06/11/2020 23:16, David Christensen:
> On 11/4/20 11:12 PM, Thomas Monjalon wrote:
> > 04/11/2020 23:25, David Christensen:
> >> On 11/4/20 1:02 PM, Thomas Monjalon wrote:
> >>> 04/11/2020 22:00, David Christensen:
> >>>> On 11/4/20 11:43 AM, Thomas Monjalon wrote:
> >>>>>> Signed-off-by: David Christensen <drc@linux.vnet.ibm.com>
> >>>>>> Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>
> >>>>>> ---
> >>>>>> -#ifdef VFIO_IOMMU_SPAPR_INFO_DDW
> >>>>>> -		/* try possible page_shift and levels for workaround */
> >>>>>> +		/* if at first we don't succeed, try more levels */
> >>>>>>     		uint32_t levels;
> >>>>>>     
> >>>>>> -		for (levels = create->levels + 1;
> >>>>>> +		for (levels = create.levels + 1;
> >>>>>>     			ret && levels <= info.ddw.levels; levels++) {
> >>>>>
> >>>>> There is a compilation failure with ppc64le-power8-linux-gcc:
> >>>>> error: ‘struct vfio_iommu_spapr_tce_info’ has no member named ‘ddw’
> >>>>
> >>>> How did you find that error?  It builds locally for me on a POWER system
> >>>> with Meson/gcc and there were no build failures on Travis
> >>>> (https://travis-ci.com/github/drchristensen/dpdk/builds/198047029) when
> >>>> I checked it against AMD64/ARM systems.  The code is PPC specific but it
> >>>> will build on all architectures (there are no IFDEFs around it).
> >>>
> >>> Remember, I cross-build with test-meson-builds.sh
> >>> Is it an issue of my toolchain?
> >>
> >> What distro/gcc version are you using?  I'll try it locally on an x86.
> > 
> > I am using powerpc64le-power8--glibc--stable-2018.11-1 from
> > https://toolchains.bootlin.com/releases_powerpc64le-power8.html
> 
> Here's what I found:
> 
> - Builds correctly on a RHEL 8.2 POWER9 host with gcc (GCC) 8.3.1 
> 20191121 (Red Hat 8.3.1-5) and kernel 4.18.0
> - Builds correctly on an Ubuntu 18.04.5 POWER9 host with gcc (Ubuntu 
> 7.5.0-3ubuntu1~18.04) 7.5.0 and kernel 4.15.0.
> - Build fails on an Ubuntu 18.04.5 AMD64 host with your POWER8 toolchain 
> and the devtools/test-meson-builds.sh script.
> 
> It appears that the VFIO header file in your toolchain:
> 
> powerpc64le-buildroot-linux-gnu/sysroot/usr/include/linux/vfio.h
> 
> is from the 4.1.49 kernel, but the sPAPR v2 IOMMU support wasn't added 
> until the 4.2.0 kernel (https://lkml.org/lkml/2015/4/25/56).  The update 
> added the ddw member to the vfio_iommu_spapr_tce_info structure.  I'll 
> submit a new patch which skips testing additional levels unless kernel 
> 4.2.0 or later is used.

Instead of testing kernel version, which is fragile with backports,
can you test the presence of the feature itself?
If no macro (usable with #ifdef) is defined with the feature,
checking the kernel version is acceptable.