From 6b6b8a63713cf730a3793b7715be0470d6152191 Mon Sep 17 00:00:00 2001
From: Mark Thompson <sw@jkqxz.net>
Date: Mon, 6 May 2019 15:43:04 +0100
Subject: [PATCH] hwcontext_vaapi: Make default DRM device selection more
 helpful

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 | 80 ++++++++++++++++++++++++++++---------
 1 file changed, 62 insertions(+), 18 deletions(-)

diff --git a/libavutil/hwcontext_vaapi.c b/libavutil/hwcontext_vaapi.c
index 561b82fcce..941c257b1b 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);
-        } 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;
+    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;
             }
-
-            av_log(ctx, AV_LOG_VERBOSE, "Opened VA display via "
-                   "DRM device %s.\n", path);
+        } else {
+            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);
+                    break;
+                }
+#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;
         }
+
+        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