android: mm: Stub libhardware for build tests

Commit 66c618f378aa ("android: mm: generic: use
GRALLOC_HARDWARE_MODULE_ID") made libhardware a required dependency for
the Android camera HAL on non-Chrome OS platforms. This isn't an issue
for real devices, as Android provides libhardware, but it prevents
compile-testing the camera HAL on traditional Linux systems.

To restore the compile-test coverage, stub the libhardware function used
by the camera HAL when libhardware isn't found.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Tested-by: Mattijs Korpershoek <mkorpershoek@baylibre.com> # meson build test
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/android/mm/libhardware_stub.c

@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: Apache-2.0 */
+/*
+ * Copyright (C) 2023, Ideas on Board
+ *
+ * libhardware_stub.c - Android libhardware stub for test compilation
+ */
+
+#include <errno.h>
+
+#include <hardware/hardware.h>
+
+int hw_get_module(const char *id __attribute__((__unused__)),
+		  const struct hw_module_t **module)
+{
+	*module = NULL;
+	return -ENOTSUP;
+}

src/android/mm/meson.build

@@ -4,10 +4,14 @@ platform = get_option('android_platform')
 if platform == 'generic'
     android_hal_sources += files(['generic_camera_buffer.cpp',
                                   'generic_frame_buffer_allocator.cpp'])
-    android_deps += [
-        libdl,
-        dependency('libhardware'),
-    ]
+    android_deps += [libdl]
+
+    libhardware = dependency('libhardware', required : false)
+    if libhardware.found()
+        android_deps += [libhardware]
+    else
+        android_hal_sources += files(['libhardware_stub.c'])
+    endif
 elif platform == 'cros'
     android_hal_sources += files(['cros_camera_buffer.cpp',
                                   'cros_frame_buffer_allocator.cpp'])