Update MPICH default version in CMakeLists and provide additional information on MPI & MPICH support in the documentation

Author: marc-joos

CMakeLists.txt

@@ -51,7 +51,7 @@ option(WI4MPI_TIMEOUT "Activate timeout")
 option(WI4MPI_GENERATOR "Enable sources generation (headers and code)" OFF)
 set(WI4MPI_GENERATOR_OPENMPI_VERSION "4.1.6" CACHE STRING "Open MPI version")
 set(WI4MPI_GENERATOR_INTELMPI_VERSION "20.0.0" CACHE STRING "Intel MPI version")
-set(WI4MPI_GENERATOR_MPICH_VERSION "4.2.0" CACHE STRING "MPICH version")
+set(WI4MPI_GENERATOR_MPICH_VERSION "3.4.3" CACHE STRING "MPICH version")
 set(WI4MPI_GENERATOR_MPI_NORM "3.1" CACHE STRING "MPI norm version")
 
 #The Rpath Strikes Back

doc/source/limitations.rst

@@ -58,3 +58,9 @@ does not fully support ``MPIX_`` functions**; this support is provided on a case
 At momment, **MPIX_Query_cuda_support** is supported. The support of other functions will
 be evaluated on demand.
 
+MPI norm support and consequences
+=================================
+
+Wi4MPI supports MPI 3.1 at the moment. This means that functions introduced in later versions are not supported.
+
+It also has an impact on the supported MPICH versions, in particular with Fortran: `f2c/f2c` functions implementation requirements changed in MPI 4.1 and this creates incompatibilities with MPICH 4.x or higher. Since MPICH versions are ABI compatible, a reasonable workaround is to generate sources for MPICH/3.x -- that is what is done at the moment.