/sys/class/drm/renderD*/device/device is Linux-only, so use a BSD extension
to get vendor/device identifiers from rendor nodes. Based on libdrm code.

According to https://github.com/intel/libva/issues/540 some nodes maybe
missing, so unlike Linux keep searching in case iGPU is older than dGPU.
mfxloader.cpp later uses the newest GPU to decide the default.

$ ffmpeg -hide_banner -init_hw_device qsv=auto -i foo.y4m -vf hwupload=extra_hw_frames=64,format=qsv -c:v h264_qsv -y foo.mkv
[AVHWDeviceContext @ 0x8062d0140] Error initializing an MFX session: -3.
Device creation failed: -1313558101.
Failed to set value 'qsv=auto' for option 'init_hw_device': Unknown error occurred
Error parsing global options: Unknown error occurred

--- api/mfx_dispatch/linux/device_ids.h.orig	2021-10-26 06:00:35 UTC
+++ api/mfx_dispatch/linux/device_ids.h
@@ -404,7 +404,62 @@ static inline eMFXHWType get_platform(int device_id) {
     return MFX_HW_UNKNOWN;
 }
 
+#if defined(__DragonFly__) || defined(__FreeBSD__) || defined(__OpenBSD__)
+#if defined(__FreeBSD__) && __FreeBSD__ < 13
+#include <sys/sysctl.h>
+#else
+#include <sys/ioctl.h>
+#include <fcntl.h>
+#include <unistd.h>
+#endif // defined(__FreeBSD__) && __FreeBSD__ < 13
+
+struct drm_pciinfo {
+	uint16_t	domain;
+	uint8_t		bus;
+	uint8_t		dev;
+	uint8_t		func;
+	uint16_t	vendor_id;
+	uint16_t	device_id;
+	uint16_t	subvendor_id;
+	uint16_t	subdevice_id;
+	uint8_t		revision_id;
+};
+
+#define DRM_IOCTL_BASE		'd'
+#define DRM_IOR(nr,type)	_IOR(DRM_IOCTL_BASE,nr,type)
+#define DRM_IOCTL_GET_PCIINFO	DRM_IOR(0x15, struct drm_pciinfo)
+#endif
+
 std::vector <Device> get_devices() {
+#ifdef DRM_IOCTL_GET_PCIINFO
+    std::vector <Device> result;
+    for (int i = 0; i < 64; ++i) {
+#if defined(__FreeBSD__) && __FreeBSD__ < 13
+        std::string mib = "dev.drm." + std::to_string(128 + i) + ".PCI_ID";
+        char pci_id[20];
+        size_t len = sizeof(pci_id);
+        if (sysctlbyname(mib.c_str(), pci_id, &len, NULL, 0)) continue;
+        Device device;
+        sscanf(pci_id, "%x:%x", &device.vendor_id, &device.device_id);
+#else
+        std::string path = "/dev/dri/renderD" + std::to_string(128 + i);
+        int fd = open(path.c_str(), O_RDONLY);
+        if (fd == -1) continue;
+        struct drm_pciinfo pinfo;
+        if (ioctl(fd, DRM_IOCTL_GET_PCIINFO, &pinfo)) {
+            close(fd);
+            continue;
+        }
+        Device device = { .vendor_id = pinfo.vendor_id, .device_id = pinfo.device_id };
+        close(fd);
+#endif // defined(__FreeBSD__) && __FreeBSD__ < 13
+        if (device.vendor_id != 0x8086) {  // Filter out non-Intel devices
+            continue;
+        }
+        device.platform = get_platform(device.device_id);
+        result.emplace_back(device);
+    }
+#else
     const char *dir = "/sys/class/drm";
     const char *device_id_file = "/device/device";
     const char *vendor_id_file = "/device/vendor";
@@ -431,6 +486,7 @@ std::vector <Device> get_devices() {
         device.platform = get_platform(device.device_id);
         result.emplace_back(device);
     }
+#endif
     std::sort(result.begin(), result.end(), [](const Device &a, const Device &b) {
         return a.platform < b.platform;
     });