[FFmpeg-devel] [PATCH 4/7] hwcontext_vaapi: Make default DRM device selection more helpful

[Mark Thompson]

Iterate over available render devices and pick the first one which looks
usable.  Adds an option to specify the name of the kernel driver associated
with the desired device, so that it is possible to select a specific type
of device in a multiple-device system without knowing the card numbering.

For example: -init_hw_device vaapi:,kernel_driver=amdgpu will select only
devices using the "amdgpu" driver (as used with recent AMD graphics cards).

Kernel driver selection requires libdrm to work.
---
 libavutil/hwcontext_vaapi.c | 76 +++++++++++++++++++++++++++++--------
 1 file changed, 60 insertions(+), 16 deletions(-)

diff --git a/libavutil/hwcontext_vaapi.c b/libavutil/hwcontext_vaapi.c
index 561b82fcce..c151f8da93 100644
--- a/libavutil/hwcontext_vaapi.c
+++ b/libavutil/hwcontext_vaapi.c
@@ -27,6 +27,7 @@
 
 #if CONFIG_LIBDRM
 #   include <va/va_drmcommon.h>
+#   include <xf86drm.h>
 #   include <drm_fourcc.h>
 #   ifndef DRM_FORMAT_MOD_INVALID
 #       define DRM_FORMAT_MOD_INVALID ((1ULL << 56) - 1)
@@ -1521,26 +1522,69 @@ static int vaapi_device_create(AVHWDeviceContext *ctx, const char *device,
 #endif
 
 #if HAVE_VAAPI_DRM
-    if (!display && try_drm) {
-        // Try to open the device as a DRM path.
-        // Default to using the first render node if the user did not
-        // supply a path.
-        const char *path = device ? device : "/dev/dri/renderD128";
-        priv->drm_fd = open(path, O_RDWR);
-        if (priv->drm_fd < 0) {
-            av_log(ctx, AV_LOG_VERBOSE, "Cannot open DRM device %s.\n",
-                   path);
+    while (!display && try_drm) {
+        // If the device is specified, try to open it as a DRM device node.
+        // If not, look for a usable render node, possibly restricted to those
+        // using a specified kernel driver.
+        int loglevel = try_all ? AV_LOG_VERBOSE : AV_LOG_ERROR;
+        if (device) {
+            priv->drm_fd = open(device, O_RDWR);
+            if (priv->drm_fd < 0) {
+                av_log(ctx, loglevel, "Failed to open %s as "
+                       "DRM device node.\n", device);
+                break;
+            }
         } else {
-            display = vaGetDisplayDRM(priv->drm_fd);
-            if (!display) {
-                av_log(ctx, AV_LOG_ERROR, "Cannot open a VA display "
-                       "from DRM device %s.\n", path);
-                return AVERROR_UNKNOWN;
+            const AVDictionaryEntry *kernel_driver;
+            char path[64];
+            int n, max_devices = 8;
+            kernel_driver = av_dict_get(opts, "kernel_driver", NULL, 0);
+            for (n = 0; n < max_devices; n++) {
+                snprintf(path, sizeof(path),
+                         "/dev/dri/renderD%d", 128 + n);
+                priv->drm_fd = open(path, O_RDWR);
+                if (priv->drm_fd < 0) {
+                    av_log(ctx, AV_LOG_VERBOSE, "Cannot open "
+                           "DRM render node for device %d.\n", n);
+                    continue;
+                }
+#if CONFIG_LIBDRM
+                if (kernel_driver) {
+                    drmVersion *info;
+                    info = drmGetVersion(priv->drm_fd);
+                    if (strcmp(kernel_driver->value, info->name)) {
+                        av_log(ctx, AV_LOG_VERBOSE, "Ignoring device %d "
+                               "with non-matching kernel driver (%s).\n",
+                               n, info->name);
+                        drmFreeVersion(info);
+                        close(priv->drm_fd);
+                        priv->drm_fd = -1;
+                        continue;
+                    }
+                    av_log(ctx, AV_LOG_VERBOSE, "Trying to use "
+                           "DRM render node for device %d, "
+                           "with matching kernel driver (%s).\n",
+                           n, info->name);
+                    drmFreeVersion(info);
+                } else
+#endif
+                {
+                    av_log(ctx, AV_LOG_VERBOSE, "Trying to use "
+                           "DRM render node for device %d.\n", n);
+                }
+                break;
             }
+            if (n >= max_devices)
+                break;
+        }
 
-            av_log(ctx, AV_LOG_VERBOSE, "Opened VA display via "
-                   "DRM device %s.\n", path);
+        display = vaGetDisplayDRM(priv->drm_fd);
+        if (!display) {
+            av_log(ctx, AV_LOG_VERBOSE, "Cannot open a VA display "
+                   "from DRM device %s.\n", device);
+            return AVERROR_EXTERNAL;
         }
+        break;
     }
 #endif
 
-- 
2.20.1