hwcontext_drm: issue DMA_BUF_IOCTL_SYNC when mapping FDs

This improves performance and helps a little when given FDs without
any synchronization fences.

libavutil/hwcontext_drm.c

@@ -19,6 +19,8 @@
 #include <fcntl.h>
 #include <sys/mman.h>
 #include <unistd.h>
+#include <linux/dma-buf.h>
+#include <sys/ioctl.h>
 
 #include <drm.h>
 #include <xf86drm.h>
@@ -85,6 +87,8 @@ static int drm_get_buffer(AVHWFramesContext *hwfc, AVFrame *frame)
 typedef struct DRMMapping {
     // Address and length of each mmap()ed region.
     int nb_regions;
+    int sync_flags;
+    int object[AV_DRM_MAX_PLANES];
     void *address[AV_DRM_MAX_PLANES];
     size_t length[AV_DRM_MAX_PLANES];
 } DRMMapping;
@@ -93,10 +97,16 @@ static void drm_unmap_frame(AVHWFramesContext *hwfc,
                             HWMapDescriptor *hwmap)
 {
     DRMMapping *map = hwmap->priv;
-    int i;
-
-    for (i = 0; i < map->nb_regions; i++)
+    struct dma_buf_sync sync = { .flags = DMA_BUF_SYNC_END | map->sync_flags };
+    int i, ret;
+
+    for (i = 0; i < map->nb_regions; i++) {
+        ret = ioctl(map->object[i], DMA_BUF_IOCTL_SYNC, &sync);
+        if (ret)
+            av_log(hwfc, AV_LOG_ERROR, "Failed to issue ioctl sync to DRM object "
+                   "%d: %d.\n", map->object[i], errno);
         munmap(map->address[i], map->length[i]);
+    }
 
     av_free(map);
 }
@@ -105,6 +115,7 @@ static int drm_map_frame(AVHWFramesContext *hwfc,
                          AVFrame *dst, const AVFrame *src, int flags)
 {
     const AVDRMFrameDescriptor *desc = (AVDRMFrameDescriptor*)src->data[0];
+    struct dma_buf_sync sync_start = { 0 };
     DRMMapping *map;
     int err, i, p, plane;
     int mmap_prot;
@@ -115,10 +126,16 @@ static int drm_map_frame(AVHWFramesContext *hwfc,
         return AVERROR(ENOMEM);
 
     mmap_prot = 0;
-    if (flags & AV_HWFRAME_MAP_READ)
+    if (flags & AV_HWFRAME_MAP_READ) {
         mmap_prot |= PROT_READ;
-    if (flags & AV_HWFRAME_MAP_WRITE)
+        map->sync_flags |= DMA_BUF_SYNC_READ;
+    }
+    if (flags & AV_HWFRAME_MAP_WRITE) {
         mmap_prot |= PROT_WRITE;
+        map->sync_flags |= DMA_BUF_SYNC_WRITE;
+    }
+
+    sync_start.flags = DMA_BUF_SYNC_START | map->sync_flags;
 
     av_assert0(desc->nb_objects <= AV_DRM_MAX_PLANES);
     for (i = 0; i < desc->nb_objects; i++) {
@@ -133,6 +150,15 @@ static int drm_map_frame(AVHWFramesContext *hwfc,
 
         map->address[i] = addr;
         map->length[i]  = desc->objects[i].size;
+        map->object[i] = desc->objects[i].fd;
+
+        err = ioctl(desc->objects[i].fd, DMA_BUF_IOCTL_SYNC, &sync_start);
+        if (err) {
+            err = AVERROR(errno);
+            av_log(hwfc, AV_LOG_ERROR, "Failed to issue ioctl sync to DRM object "
+                   "%d: %d.\n", desc->objects[i].fd, errno);
+            goto fail;
+        }
     }
     map->nb_regions = i;