daedalus_v4l2: meson option gate (default true)

Adds a build-time switch so platforms that will never see a
daedalus_v4l2 kernel module (Allwinner cedrus, RK without the
shim, etc.) can opt out of the probe entry + dispatch branch.

  meson setup build                         # daedalus support on
  meson setup build-off -Ddaedalus_v4l2=false  # off

Implementation:
- meson_options.txt: new boolean `daedalus_v4l2`, default true.
- src/meson.build: when option is true, autoconfig.h gets
  `#define HAVE_DAEDALUS_V4L2 1`.
- src/request.c: known_decoder_drivers[] entry, primary-driver
  detection branch, and post-probe log line all gated by
  #ifdef HAVE_DAEDALUS_V4L2.
- src/request.h: struct daedalus fields kept UNCONDITIONAL.
  Two extra int per session and the struct layout stays stable
  across translation units regardless of option — avoids the
  ODR risk of every consumer of request.h needing to include
  autoconfig.h before request.h.

Verified on hertz: both builds compile clean.
  build/src/autoconfig.h has HAVE_DAEDALUS_V4L2; .so contains
  "daedalus_v4l2" string + log message.
  build-off/src/autoconfig.h doesn't; .so contains no daedalus
  strings at all.

Default-on build still passes vainfo end-to-end:
  vainfo: Driver version: v4l2-request
  vainfo: Supported profile and entrypoints
        VAProfileH264Main / High / ConstrainedBaseline / MultiviewHigh
        / StereoHigh : VAEntrypointVLD
        VAProfileVP9Profile0 : VAEntrypointVLD
        VAProfileAV1Profile0 : VAEntrypointVLD

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

meson_options.txt

@@ -4,3 +4,14 @@ option(
     value : '',
     description: 'Path to sanitized Linux Kernel headers'
 )
+
+option(
+    'daedalus_v4l2',
+    type : 'boolean',
+    value : true,
+    description: 'Enable probe + dispatch for the out-of-tree daedalus_v4l2 ' +
+                 'stateless decoder shim (Pi 5 / CM5 daemon-backed VP9/AV1/H264). ' +
+                 'Default true; disable on platforms where the daedalus_v4l2 ' +
+                 'kernel module will never be present to slim the probe array.'
+)
+

src/meson.build

@@ -22,6 +22,9 @@
 
 autoconf_data = configuration_data()
 autoconf_data.set('VA_DRIVER_INIT_FUNC', va_driver_init_func)
+if get_option('daedalus_v4l2')
+	autoconf_data.set('HAVE_DAEDALUS_V4L2', 1)
+endif
 
 autoconf = configure_file(
 	output: 'autoconfig.h',

src/request.c

@@ -94,7 +94,9 @@ static const char * const known_decoder_drivers[] = {
 	"rkvdec",
 	"hantro-vpu",
 	"rpi-hevc-dec",  /* iter40: Pi 5 / CM5 stateless HEVC */
+#ifdef HAVE_DAEDALUS_V4L2
 	"daedalus_v4l2", /* phase 8.10: Pi 5 daemon-backed VP9/AV1/H264 */
+#endif
 	"cedrus",
 	"sun4i_csi",
 	NULL
@@ -703,6 +705,7 @@ VAStatus VA_DRIVER_INIT_FUNC(VADriverContextP context)
 				alt_driver = NULL;
 				driver_data->video_fd_rpi_hevc_dec = video_fd;
 				driver_data->media_fd_rpi_hevc_dec = media_fd;
+#ifdef HAVE_DAEDALUS_V4L2
 			} else if (strcmp(info.driver, "daedalus_v4l2") == 0) {
 				/* phase 8.10: Pi 5 daemon-backed decoder.  Sole
 				 * V4L2 stateless slot on this kernel; VP9 / AV1 /
@@ -716,6 +719,7 @@ VAStatus VA_DRIVER_INIT_FUNC(VADriverContextP context)
 				alt_driver = NULL;
 				driver_data->video_fd_daedalus = video_fd;
 				driver_data->media_fd_daedalus = media_fd;
+#endif
 			}
 		}
 
@@ -823,12 +827,14 @@ VAStatus VA_DRIVER_INIT_FUNC(VADriverContextP context)
 			    driver_data->video_fd_rpi_hevc_dec,
 			    driver_data->media_fd_rpi_hevc_dec);
 	}
+#ifdef HAVE_DAEDALUS_V4L2
 	if (driver_data->video_fd_daedalus >= 0) {
 		request_log("phase 8.10: opened daedalus_v4l2 at video_fd=%d "
 			    "media_fd=%d (Pi 5 daemon-backed VP9/AV1/H264)\n",
 			    driver_data->video_fd_daedalus,
 			    driver_data->media_fd_daedalus);
 	}
+#endif
 
 	status = VA_STATUS_SUCCESS;
 	goto complete;

src/request.h

@@ -105,6 +105,12 @@ struct request_data {
 	 * same media-controller probe + known_decoder_drivers[] entry
 	 * pattern as iter40 rpi-hevc-dec.  Stays -1 on hosts without the
 	 * daedalus module loaded; HEVC routes to rpi-hevc-dec as before.
+	 *
+	 * Fields are unconditional (8 bytes per session) so the struct
+	 * layout is stable regardless of meson option.  The active
+	 * probe + dispatch code in request.c is gated by
+	 * HAVE_DAEDALUS_V4L2; when disabled the fields stay at their
+	 * -1 init and no codepath touches them.
 	 */
 	int video_fd_daedalus;
 	int media_fd_daedalus;