Add libva-v4l2-request-ohm-gl-fix package

Mirrors phase6/step1/ from the ohm_gl_fix campaign. Contract-correct
hantro multi-planar / chromium-149-era stateless H.264 port of
bootlin's libva-v4l2-request, patches 0001..0018 + fourier-local.

Honest characterisation in README:
  - Builds cleanly on chromium-builder LXC (boltzmann)
  - vainfo enumerates H.264 profiles cleanly with LIBVA_DRIVER_NAME=v4l2_request
  - NOT on Brave's decode path on ohm_gl_fix stack — Brave uses
    Chromium's own V4L2VideoDecoder in media/gpu/v4l2/.
  - Most likely useful for a future Firefox-via-libavcodec-vaapi
    campaign, modulo a separate Mesa-panfrost WSI pitch issue.
  - DEBUG patches (0010, 0011, 0014) intentionally kept in series
    for development; remove for cleaner production runs.

Audit trail in the source repo at ohm_gl_fix:
  phase6/step1/audit_0008_decode_params_2026-05-01.md
  phase6/step1/api_contract_findings_2026-05-01.md
  phase3_remeasure_2026-05-02/B3_decoder_discovery.md (why this
    isn't on Brave's path)

arch/libva-v4l2-request-ohm-gl-fix/0003-v4l2-query-helpers.patch

@@ -0,0 +1,145 @@
+From: Markus Fritsche <fritsche.markus@gmail.com>
+Date: 2026-05-01
+Subject: [PATCH] v4l2: add QUERYCTRL/QUERYMENU capability-probe helpers
+
+Pure utility additions, no behaviour change. Three helpers in
+src/v4l2.{c,h}:
+
+  - v4l2_query_ext_ctrl(): wraps VIDIOC_QUERY_EXT_CTRL by CID.
+    Returns 0 if the control exists, -1 if not. Caller passes NULL
+    qec to test existence only.
+
+  - v4l2_query_menu(): wraps VIDIOC_QUERYMENU at a given index.
+    Returns 0 if a menu item exists at that index, -1 otherwise.
+
+  - v4l2_ctrl_menu_has_value(): convenience layered on the above.
+    For a menu/intmenu-type control, walks all menu items between
+    minimum and maximum and returns true iff `value` is a valid
+    entry. Used by callers that ask "does this driver accept menu
+    value X for this CID?" without caring about iteration details.
+
+These unblock commit 3 (request_pool — needs ext-ctrl probing for
+codec-ops dispatch) and commit 4 (probe-then-set DECODE_MODE/
+START_CODE — replaces 0002's unconditional set with a real probe)
+of the upstreamable design's six-commit series.
+
+Forward-declarations in v4l2.h keep the header lean: existing
+prototypes already use opaque struct v4l2_ext_control * pointers
+without including <linux/videodev2.h>; we follow the same
+convention for struct v4l2_query_ext_ctrl and struct v4l2_querymenu.
+
+No call sites added in this commit. Compile-only verification:
+the .so links cleanly with three new exports.
+
+Signed-off-by: Markus Fritsche <fritsche.markus@gmail.com>
+---
+ src/v4l2.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ src/v4l2.h | 33 +++++++++++++++++++++++++++++
+ 2 files changed, 93 insertions(+)
+
+--- a/src/v4l2.h
++++ b/src/v4l2.h
+@@ -64,4 +64,37 @@ int v4l2_set_control(int video_fd, int request_fd, unsigned int id, void *data,
+ 		     unsigned int size);
+ int v4l2_set_stream(int video_fd, unsigned int type, bool enable);
+
++/*
++ * Capability-probe helpers. These let calling code discover what the
++ * backing kernel driver supports rather than hardcoding assumptions
++ * about specific decoder hardware.
++ */
++
++/*
++ * Query the metadata of an extended control by CID. Fills *qec on
++ * success. Returns 0 if the control exists, -1 (errno=EINVAL) if the
++ * driver does not expose this CID. Pass qec=NULL to test existence
++ * only.
++ */
++struct v4l2_query_ext_ctrl;
++int v4l2_query_ext_ctrl(int video_fd, unsigned int id,
++			struct v4l2_query_ext_ctrl *qec);
++
++/*
++ * Query a single menu item of a menu/intmenu control at the given
++ * index. Fills *qm on success. Returns 0 if the menu item exists at
++ * this index, -1 otherwise.
++ */
++struct v4l2_querymenu;
++int v4l2_query_menu(int video_fd, unsigned int id, unsigned int index,
++		    struct v4l2_querymenu *qm);
++
++/*
++ * Convenience: for a menu-type control, return true iff `value` is a
++ * valid menu entry (i.e. the driver accepts it). Walks all menu items
++ * up to the control's maximum to check.
++ */
++bool v4l2_ctrl_menu_has_value(int video_fd, unsigned int id,
++			      unsigned int value);
++
+ #endif
+--- a/src/v4l2.c
++++ b/src/v4l2.c
+@@ -508,3 +508,63 @@ int v4l2_set_stream(int video_fd, unsigned int type, bool enable)
+
+ 	return 0;
+ }
++
++int v4l2_query_ext_ctrl(int video_fd, unsigned int id,
++			struct v4l2_query_ext_ctrl *qec)
++{
++	struct v4l2_query_ext_ctrl local;
++	struct v4l2_query_ext_ctrl *target = qec ? qec : &local;
++	int rc;
++
++	memset(target, 0, sizeof(*target));
++	target->id = id;
++
++	rc = ioctl(video_fd, VIDIOC_QUERY_EXT_CTRL, target);
++	if (rc < 0)
++		return -1;
++
++	return 0;
++}
++
++int v4l2_query_menu(int video_fd, unsigned int id, unsigned int index,
++		    struct v4l2_querymenu *qm)
++{
++	int rc;
++
++	if (qm == NULL)
++		return -1;
++
++	memset(qm, 0, sizeof(*qm));
++	qm->id = id;
++	qm->index = index;
++
++	rc = ioctl(video_fd, VIDIOC_QUERYMENU, qm);
++	if (rc < 0)
++		return -1;
++
++	return 0;
++}
++
++bool v4l2_ctrl_menu_has_value(int video_fd, unsigned int id,
++			      unsigned int value)
++{
++	struct v4l2_query_ext_ctrl qec;
++	struct v4l2_querymenu qm;
++	long long i;
++
++	if (v4l2_query_ext_ctrl(video_fd, id, &qec) < 0)
++		return false;
++
++	if (qec.type != V4L2_CTRL_TYPE_MENU &&
++	    qec.type != V4L2_CTRL_TYPE_INTEGER_MENU)
++		return false;
++
++	for (i = qec.minimum; i <= qec.maximum; i += qec.step ? qec.step : 1) {
++		if (v4l2_query_menu(video_fd, id, (unsigned int)i, &qm) < 0)
++			continue;
++		if ((unsigned int)i == value)
++			return true;
++	}
++
++	return false;
++}