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fresnel-fourier iter4 Phase 6 commit Z: device-path auto-detect via media controller topology

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Pre-iter4 backend hardcoded /dev/video0 + /dev/media0 as defaults
when no env override was set. Linux 7.0 udev/probe order changed,
rockchip-rga (RGB color converter, no codec) now claims
/dev/video0 — legacy default returns empty profile list.

Discovery is driven by the media controller graph (the canonical
v4l2-request approach). NOT a /dev/video* walk by enumeration
order — that mispairs video and media nodes when one driver
registers multiple media devices, and depends on probe-order
luck.

Algorithm:
  1. Walk /dev/media0..15. MEDIA_IOC_DEVICE_INFO names the driver.
     Match against {rkvdec, hantro-vpu, cedrus, sun4i_csi}.
  2. MEDIA_IOC_G_TOPOLOGY enumerates the entity/interface graph.
     The MEDIA_INTF_T_V4L_VIDEO interface carries major:minor of
     the V4L2 video node owned by THIS media controller — paired
     by the kernel, not by /dev/* enumeration order.
  3. Resolve major:minor to /dev/videoN via /sys/dev/char/<M>:<N>
     (the kernel's char-device sysfs symlink whose basename is
     the device node name).

LIBVA_V4L2_REQUEST_NO_AUTODETECT=1 escape hatch reverts to legacy
/dev/video0 + /dev/media0 hardcoded behavior for callers that
depended on it.

Phase 5 C4 amendment: walk-and-pick-first selects rkvdec on RK3399
(rkvdec's media controller enumerates before hantro's). H.264 /
HEVC / VP9 (rkvdec codecs) work without env override after this
commit. MPEG-2 / VP8 (hantro) still require explicit
LIBVA_V4L2_REQUEST_VIDEO_PATH=/dev/video3 override; full
multi-decoder dispatch is iter4-B1 backlog item.

Verified empirically on fresnel (linux-fresnel-fourier 7.0-1):
- vainfo (no env) -> "auto-selected codec device: /dev/video1 +
  /dev/media0", enumerates H264*5 + HEVCMain (rkvdec) — paired
  via topology graph, not /dev/video* enumeration.
- vainfo NO_AUTODETECT=1 -> empty list (legacy /dev/video0 = rga).
- vainfo with explicit /dev/video3 + /dev/media1 -> MPEG2*2 + VP8.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Claude (noether)
2026-05-10 06:00:56 +00:00
parent e1aca9cc6b
commit 7f8fa93213
1 changed files with 152 additions and 4 deletions
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src/request.c
+152 -4
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@@ -41,6 +41,7 @@
#include "v4l2.h"
#include <assert.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
@@ -51,8 +52,137 @@
#include <sys/ioctl.h>
#include <linux/media.h>
#include <linux/videodev2.h>
/*
* fresnel-fourier iter4 Phase 6 commit Z: device-path auto-detect via media controller topology
*
* Pre-iter4 the backend hardcoded /dev/video0 + /dev/media0 as defaults
* when no env override was set. On Linux 7.0 the udev/probe order
* changed and rockchip-rga (an RGB color converter, no codec support)
* now claims /dev/video0 — the legacy default returns an empty profile
* list.
*
* Discovery is driven by the media controller graph (NOT by walking
* /dev/video* in enumeration order — that approach can mispair the
* video and media nodes when one driver registers multiple media
* devices, and depends on probe-order luck):
*
* 1. Walk /dev/media0..N. For each, MEDIA_IOC_DEVICE_INFO names the
* driver. Match against the known-decoder list.
* 2. MEDIA_IOC_G_TOPOLOGY returns the entity/interface graph. The
* MEDIA_INTF_T_V4L_VIDEO interface entries carry major:minor of
* the V4L2 video node owned by THIS media controller — guaranteed
* paired by the kernel.
* 3. Resolve major:minor to /dev/videoN via /sys/dev/char/<M>:<N>
* (the kernel's char-device sysfs symlink whose basename is the
* device node name).
*
* Phase 5 C4: walk picks rkvdec on RK3399 (rkvdec's media controller
* enumerates before hantro's). MPEG-2/VP8 (hantro) still need explicit
* LIBVA_V4L2_REQUEST_VIDEO_PATH override; full multi-decoder dispatch
* is iter4-B1 backlog.
*
* Escape hatch: LIBVA_V4L2_REQUEST_NO_AUTODETECT=1 reverts to legacy
* hardcoded /dev/video0 + /dev/media0 for callers that relied on it.
*/
static const char * const known_decoder_drivers[] = {
"rkvdec",
"hantro-vpu",
"cedrus",
"sun4i_csi",
NULL
};
static int resolve_dev_node(uint32_t major, uint32_t minor, char *out, size_t out_sz)
{
char sysfs_path[64], target[256];
ssize_t n;
const char *base;
snprintf(sysfs_path, sizeof sysfs_path, "/sys/dev/char/%u:%u", major, minor);
n = readlink(sysfs_path, target, sizeof target - 1);
if (n < 0)
return -1;
target[n] = '\0';
base = strrchr(target, '/');
base = base ? base + 1 : target;
snprintf(out, out_sz, "/dev/%s", base);
return 0;
}
static int find_video_node_via_topology(int media_fd, char *video_out, size_t video_out_sz)
{
struct media_v2_topology topo;
struct media_v2_interface *interfaces = NULL;
int ret = -1;
unsigned int i;
memset(&topo, 0, sizeof topo);
if (ioctl(media_fd, MEDIA_IOC_G_TOPOLOGY, &topo) < 0)
return -1;
if (topo.num_interfaces == 0)
return -1;
interfaces = calloc(topo.num_interfaces, sizeof *interfaces);
if (!interfaces)
return -1;
memset(&topo, 0, sizeof topo);
if (ioctl(media_fd, MEDIA_IOC_G_TOPOLOGY, &topo) < 0)
goto out;
topo.ptr_interfaces = (uintptr_t)interfaces;
if (ioctl(media_fd, MEDIA_IOC_G_TOPOLOGY, &topo) < 0)
goto out;
for (i = 0; i < topo.num_interfaces; i++) {
if (interfaces[i].intf_type != MEDIA_INTF_T_V4L_VIDEO)
continue;
if (resolve_dev_node(interfaces[i].devnode.major,
interfaces[i].devnode.minor,
video_out, video_out_sz) == 0) {
ret = 0;
break;
}
}
out:
free(interfaces);
return ret;
}
static int find_codec_device(char *video_out, size_t video_out_sz,
char *media_out, size_t media_out_sz)
{
struct media_device_info info;
char path[32];
const char * const *kd;
int fd, i;
for (i = 0; i < 16; i++) {
snprintf(path, sizeof path, "/dev/media%d", i);
fd = open(path, O_RDWR | O_NONBLOCK);
if (fd < 0)
continue;
memset(&info, 0, sizeof info);
if (ioctl(fd, MEDIA_IOC_DEVICE_INFO, &info) == 0) {
for (kd = known_decoder_drivers; *kd; kd++) {
if (strcmp(info.driver, *kd) != 0)
continue;
if (find_video_node_via_topology(fd, video_out,
video_out_sz) == 0) {
snprintf(media_out, media_out_sz, "%s", path);
close(fd);
return 0;
}
break;
}
}
close(fd);
}
return -1;
}
/* Set default visibility for the init function only. */
VAStatus __attribute__((visibility("default")))
VA_DRIVER_INIT_FUNC(VADriverContextP context);
@@ -146,9 +276,23 @@ VAStatus VA_DRIVER_INIT_FUNC(VADriverContextP context)
object_heap_init(&driver_data->image_heap, sizeof(struct object_image),
IMAGE_ID_OFFSET);
static char auto_video[32], auto_media[32];
bool auto_media_set = false;
video_path = getenv("LIBVA_V4L2_REQUEST_VIDEO_PATH");
if (video_path == NULL)
video_path = "/dev/video0";
if (video_path == NULL) {
if (getenv("LIBVA_V4L2_REQUEST_NO_AUTODETECT")) {
video_path = "/dev/video0";
} else if (find_codec_device(auto_video, sizeof auto_video,
auto_media, sizeof auto_media) == 0) {
video_path = auto_video;
auto_media_set = true;
request_log("auto-selected codec device: %s + %s\n",
auto_video, auto_media);
} else {
video_path = "/dev/video0";
}
}
video_fd = open(video_path, O_RDWR | O_NONBLOCK);
if (video_fd < 0)
@@ -169,8 +313,12 @@ VAStatus VA_DRIVER_INIT_FUNC(VADriverContextP context)
}
media_path = getenv("LIBVA_V4L2_REQUEST_MEDIA_PATH");
if (media_path == NULL)
media_path = "/dev/media0";
if (media_path == NULL) {
if (auto_media_set)
media_path = auto_media;
else
media_path = "/dev/media0";
}
media_fd = open(media_path, O_RDWR | O_NONBLOCK);
if (media_fd < 0)