meson: move libfdt together with other dependencies

Move the libfdt detection code together with other dependencies instead
of keeping it with subprojects.  This has the disadvantage of performing
the detection even if no target requires libfdt; but it has the advantage
that Kconfig will be able to observe the availability of the library.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

meson.build

@@ -1858,6 +1858,34 @@ if numa.found() and not cc.links('''
   endif
 endif
 
+fdt = not_found
+fdt_opt = get_option('fdt')
+if fdt_opt == 'enabled' and get_option('wrap_mode') == 'nodownload'
+  fdt_opt = 'system'
+endif
+if fdt_opt in ['enabled', 'system'] or (fdt_opt == 'auto' and have_system)
+  fdt = cc.find_library('fdt', required: fdt_opt == 'system')
+  if fdt.found() and cc.links('''
+     #include <libfdt.h>
+     #include <libfdt_env.h>
+     int main(void) { fdt_find_max_phandle(NULL, NULL); return 0; }''',
+       dependencies: fdt)
+    fdt_opt = 'system'
+  elif fdt_opt != 'system'
+    fdt_opt = get_option('wrap_mode') == 'nodownload' ? 'disabled' : 'internal'
+    fdt = not_found
+  else
+    error('system libfdt is too old (1.5.1 or newer required)')
+  endif
+endif
+if fdt_opt == 'internal'
+  assert(not fdt.found())
+  libfdt_proj = subproject('dtc', required: true,
+                           default_options: ['tools=false',  'yaml=disabled',
+                                             'python=disabled', 'default_library=static'])
+  fdt = libfdt_proj.get_variable('libfdt_dep')
+endif
+
 rdma = not_found
 if not get_option('rdma').auto() or have_system
   libumad = cc.find_library('ibumad', required: get_option('rdma'))
@@ -2199,6 +2227,7 @@ config_host_data.set('CONFIG_BSD', host_os in bsd_oses)
 config_host_data.set('CONFIG_CAPSTONE', capstone.found())
 config_host_data.set('CONFIG_COCOA', cocoa.found())
 config_host_data.set('CONFIG_DARWIN', host_os == 'darwin')
+config_host_data.set('CONFIG_FDT', fdt.found())
 config_host_data.set('CONFIG_FUZZ', get_option('fuzzing'))
 config_host_data.set('CONFIG_GCOV', get_option('b_coverage'))
 config_host_data.set('CONFIG_LIBUDEV', libudev.found())
@@ -3024,14 +3053,16 @@ foreach target : target_dirs
     error('No accelerator available for target @0@'.format(target))
   endif
 
-  actual_target_dirs += target
   config_target += keyval.load('configs/targets' / target + '.mak')
   config_target += { 'TARGET_' + config_target['TARGET_ARCH'].to_upper(): 'y' }
 
-  if 'TARGET_NEED_FDT' in config_target
+  if 'TARGET_NEED_FDT' in config_target and not fdt.found()
     fdt_required += target
+    continue
   endif
 
+  actual_target_dirs += target
+
   # Add default keys
   if 'TARGET_BASE_ARCH' not in config_target
     config_target += {'TARGET_BASE_ARCH': config_target['TARGET_ARCH']}
@@ -3119,6 +3150,10 @@ genh += custom_target('config-poison.h',
                       command: [find_program('scripts/make-config-poison.sh'),
                                 target_configs_h])
 
+if fdt_required.length() > 0
+  error('fdt disabled but required by targets ' + ', '.join(fdt_required))
+endif
+
 ###############
 # Subprojects #
 ###############
@@ -3129,44 +3164,6 @@ if have_system and vfio_user_server_allowed
   libvfio_user_dep = libvfio_user_proj.get_variable('libvfio_user_dep')
 endif
 
-fdt = not_found
-fdt_opt = get_option('fdt')
-if fdt_required.length() > 0 or fdt_opt == 'enabled'
-  if fdt_opt == 'disabled'
-    error('fdt disabled but required by targets ' + ', '.join(fdt_required))
-  endif
-
-  if fdt_opt in ['enabled', 'auto', 'system']
-    if get_option('wrap_mode') == 'nodownload'
-      fdt_opt = 'system'
-    endif
-    fdt = cc.find_library('fdt', required: fdt_opt == 'system')
-    if fdt.found() and cc.links('''
-       #include <libfdt.h>
-       #include <libfdt_env.h>
-       int main(void) { fdt_find_max_phandle(NULL, NULL); return 0; }''',
-         dependencies: fdt)
-      fdt_opt = 'system'
-    elif fdt_opt == 'system'
-       error('system libfdt requested, but it is too old (1.5.1 or newer required)')
-    else
-      fdt_opt = 'internal'
-      fdt = not_found
-    endif
-  endif
-  if not fdt.found()
-    assert(fdt_opt == 'internal')
-    libfdt_proj = subproject('dtc', required: true,
-                             default_options: ['tools=false',  'yaml=disabled',
-                                               'python=disabled', 'default_library=static'])
-    fdt = libfdt_proj.get_variable('libfdt_dep')
-  endif
-else
-  fdt_opt = 'disabled'
-endif
-
-config_host_data.set('CONFIG_FDT', fdt.found())
-
 vhost_user = not_found
 if host_os == 'linux' and have_vhost_user
   libvhost_user = subproject('libvhost-user')
@@ -4417,7 +4414,7 @@ summary_info += {'Linux AIO support': libaio}
 summary_info += {'Linux io_uring support': linux_io_uring}
 summary_info += {'ATTR/XATTR support': libattr}
 summary_info += {'RDMA support':      rdma}
-summary_info += {'fdt support':       fdt_opt == 'disabled' ? false : fdt_opt}
+summary_info += {'fdt support':       fdt_opt == 'internal' ? 'internal' : fdt}
 summary_info += {'libcap-ng support': libcap_ng}
 summary_info += {'bpf support':       libbpf}
 summary_info += {'rbd support':       rbd}