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 | 79 ++++++++++++++++++++++++++---------------------------
 1 file changed, 38 insertions(+), 41 deletions(-)

diff --git a/meson.build b/meson.build
index ab1f44b25c2..dd4a28f8f8f 100644
--- a/meson.build
+++ b/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}
-- 
2.45.0