Now for kernel 4.13:

LIBGL_DEBUG=verbose glxinfo | grep ' render'
libGL: Can't open configuration file /home/odo/.drirc: No such file or
directory.
libGL: pci id for fd 4: 1002:699f, driver radeonsi
libGL: OpenDriver: trying /usr/lib/x86_64-linux-gnu/dri/tls/radeonsi_dri.so
libGL: OpenDriver: trying /usr/lib/x86_64-linux-gnu/dri/radeonsi_dri.so
libGL: Can't open configuration file /home/odo/.drirc: No such file or
directory.
/usr/local/share/libdrm/amdgpu.ids version: 1.0.0
libGL: Can't open configuration file /home/odo/.drirc: No such file or
directory.
libGL: Using DRI3 for screen 0
direct rendering: Yes
Extended renderer info (GLX_MESA_query_renderer):
OpenGL renderer string: Radeon RX 550 Series (POLARIS12 / DRM 3.18.0 /
4.13.0-1-amd64, LLVM 3.9.1)

and

glxinfo | grep OpenGL | renderer'
OpenGL vendor string: X.Org
OpenGL renderer string: Radeon RX 550 Series (POLARIS12 / DRM 3.18.0 /
4.13.0-1-amd64, LLVM 3.9.1)
OpenGL core profile version string: 4.5 (Core Profile) Mesa 17.4.0-devel
(git-1eab327ba7)
OpenGL core profile shading language version string: 4.50
OpenGL core profile context flags: (none)
OpenGL core profile profile mask: core profile
OpenGL core profile extensions:
OpenGL version string: 3.0 Mesa 17.4.0-devel (git-1eab327ba7)
OpenGL shading language version string: 1.30
OpenGL context flags: (none)
OpenGL extensions:
OpenGL ES profile version string: OpenGL ES 3.1 Mesa 17.4.0-devel
(git-1eab327ba7)
OpenGL ES profile shading language version string: OpenGL ES GLSL ES 3.10
OpenGL ES profile extensions:

Looks good, many thanks for your help!