meson: Improve NVMM CUDA detection

1. Add some comments explaining what headers and libs are expected on
   what systems
2. Only look in default incdirs if no incdir is specified
3. Require libnvbufsurface.so on Jetson when cuda-nvmm=enabled
4. Require libatomic on Jetson when cuda-nvmm=enabled

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8021>

subprojects/gst-plugins-bad/gst-libs/gst/cuda/meson.build

@@ -40,8 +40,8 @@ if host_system not in ['windows', 'linux']
 endif
 
 # Linux ARM would need -latomic for std::atomic<int64_t>
-if host_system == 'linux' and host_machine.cpu_family() not in ['x86', 'x86_64']
+if host_system == 'linux' and host_machine.cpu_family() in ['aarch64', 'arm']
-  libatomic_dep = cxx.find_library('atomic', required: false)
+  libatomic_dep = cxx.find_library('atomic', required: get_option('cuda-nvmm'))
   if not libatomic_dep.found()
     subdir_done()
   endif
@@ -89,43 +89,52 @@ if host_system == 'windows'
     ])
   endif
 else
+  # We have NVMM with nvbufsurface.h on both Linux x86 and Jetson (aarch64)
   nvmm_opt = get_option('cuda-nvmm')
-  if not nvmm_opt.disabled()
+  fsmod = import('fs')
+  if nvmm_opt.allowed()
+    incdir_candidates = []
+
     nvmm_inc_opt = get_option('cuda-nvmm-include-path')
     if nvmm_inc_opt != ''
-      gstcuda_nvmm_inc = [include_directories(nvmm_inc_opt)]
+      incdir_candidates += [nvmm_inc_opt]
+    else
+      # try some other default locations
+      incdir_candidates = [
+        '/usr/src/jetson_multimedia_api/include',
+        '/opt/nvidia/deepstream/deepstream/sources/includes',
+      ]
     endif
 
+    foreach incdir: incdir_candidates
+      if fsmod.is_dir(incdir)
+        incdir = include_directories(incdir)
         if cc.has_header('nvbufsurface.h',
-                     include_directories: gstcuda_nvmm_inc,
+                         include_directories: incdir,
                          required: false)
           have_nvbufsurface_h = true
-    # try some other default locations
+          gstcuda_nvmm_inc = incdir
-    elif cc.has_header('/usr/src/jetson_multimedia_api/include/nvbufsurface.h',
+          break
-	               required: false)
-      have_nvbufsurface_h = true
-      gstcuda_nvmm_inc = [include_directories('/usr/src/jetson_multimedia_api/include')]
-    elif cc.has_header('/opt/nvidia/deepstream/deepstream/sources/includes/nvbufsurface.h',
-                       required: false)
-      have_nvbufsurface_h = true
-      gstcuda_nvmm_inc = [include_directories('/opt/nvidia/deepstream/deepstream/sources/includes')]
-    endif
-    if nvmm_opt.enabled() and not have_nvbufsurface_h
-      error('Could not find required header: "nvbufsurface.h"')
-      subdir_done()
         endif
       endif
+    endforeach
 
     if have_nvbufsurface_h
       extra_args += ['-DHAVE_CUDA_NVMM']
-
+      # On Tegra, we also have libnvbufsurface.so, which is not present on x86
+      if host_machine.cpu_family() == 'aarch64'
         # check if we have a tegra based system (jetson)
-    nvbuf_dep = cc.find_library('nvbufsurface', dirs: '/usr/lib/aarch64-linux-gnu/tegra/', required: false)
+        nvbuf_dep = cc.find_library('nvbufsurface', dirs: '/usr/lib/aarch64-linux-gnu/tegra/', required: nvmm_opt)
         if nvbuf_dep.found()
           extra_deps += [nvbuf_dep]
           extra_args += ['-DHAVE_CUDA_NVMM_JETSON']
         endif
       endif
+    elif nvmm_opt.enabled()
+      error('Could not find required header: "nvbufsurface.h"')
+      subdir_done()
+    endif
+  endif
 endif
 
 pkg_name = 'gstreamer-cuda-' + api_version