To further facilitate GEM testing, allow testing of drm_syncobj by
attaching them to vgem fences. These fences are already employed by igt
for testing inter-driver fence handling (across dmabuf and sync_file).

An igt example use would be like:

   int vgem = drm_driver_open(DRIVER_VGEM);
   uint32_t handle = vgem_create_dummy(vgem);
   uint32_t syncobj = drm_syncobj_create(vgem);
   uint32_t fence = drmIoctl(vgem,
                             DRM_IOCTL_VGEM_FENCE_ATTACH,
                             &(struct vgem_fence_attach){
                                .handle = handle,
                                .flags = VGEM_FENCE_SYNCOBJ,
                                .syncobj = syncobj,
                             });

   /* ... use syncobj for profit ... */

   vgem_fence_signal(vgem, fence);

For wider use though, there is little immediate benefit to syncobj
over the vgem fence as both are handles in an idr (the fence here is not
a sync-file fd like in most other drivers). The main benefit for syncobj
is that it allows to create channels between objects and drivers by
virtue of its persistence beyond the vgem fence itself.

Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
Cc: Jason Ekstrand <ja...@jlekstrand.net>
Cc: Daniel Vetter <daniel.vet...@ffwll.ch>
---
 drivers/gpu/drm/vgem/vgem_drv.c   |  4 +++-
 drivers/gpu/drm/vgem/vgem_fence.c | 26 ++++++++++++++++++++++----
 include/drm/drm_syncobj.h         |  2 ++
 include/uapi/drm/vgem_drm.h       |  3 ++-
 4 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/vgem/vgem_drv.c b/drivers/gpu/drm/vgem/vgem_drv.c
index 12289673f457..a0202e1eaf6b 100644
--- a/drivers/gpu/drm/vgem/vgem_drv.c
+++ b/drivers/gpu/drm/vgem/vgem_drv.c
@@ -432,7 +432,9 @@ static void vgem_release(struct drm_device *dev)
 }
 
 static struct drm_driver vgem_driver = {
-       .driver_features                = DRIVER_GEM | DRIVER_PRIME,
+       .driver_features                = (DRIVER_GEM |
+                                          DRIVER_PRIME |
+                                          DRIVER_SYNCOBJ),
        .release                        = vgem_release,
        .open                           = vgem_open,
        .postclose                      = vgem_postclose,
diff --git a/drivers/gpu/drm/vgem/vgem_fence.c 
b/drivers/gpu/drm/vgem/vgem_fence.c
index 3109c8308eb5..988e860c03d3 100644
--- a/drivers/gpu/drm/vgem/vgem_fence.c
+++ b/drivers/gpu/drm/vgem/vgem_fence.c
@@ -23,6 +23,8 @@
 #include <linux/dma-buf.h>
 #include <linux/reservation.h>
 
+#include <drm/drm_syncobj.h>
+
 #include "vgem_drv.h"
 
 #define VGEM_FENCE_TIMEOUT (10*HZ)
@@ -156,20 +158,30 @@ int vgem_fence_attach_ioctl(struct drm_device *dev,
        struct drm_vgem_fence_attach *arg = data;
        struct vgem_file *vfile = file->driver_priv;
        struct reservation_object *resv;
+       struct drm_syncobj *sync = NULL;
        struct drm_gem_object *obj;
        struct dma_fence *fence;
        int ret;
 
-       if (arg->flags & ~VGEM_FENCE_WRITE)
-               return -EINVAL;
-
-       if (arg->pad)
+       if (arg->flags & ~(VGEM_FENCE_WRITE | VGEM_FENCE_SYNCOBJ))
                return -EINVAL;
 
        obj = drm_gem_object_lookup(file, arg->handle);
        if (!obj)
                return -ENOENT;
 
+       if (arg->flags & VGEM_FENCE_SYNCOBJ) {
+               sync = drm_syncobj_find(file, arg->syncobj);
+               if (!sync) {
+                       ret = -ENOENT;
+                       goto err;
+               }
+
+               /* We don't check if the current syncobj is busy or not, we
+                * will just replace it with ourselves.
+                */
+       }
+
        ret = attach_dmabuf(dev, obj);
        if (ret)
                goto err;
@@ -207,12 +219,18 @@ int vgem_fence_attach_ioctl(struct drm_device *dev,
                        ret = 0;
                }
        }
+
+       if (ret == 0 && sync)
+               drm_syncobj_replace_fence(sync, fence);
+
 err_fence:
        if (ret) {
                dma_fence_signal(fence);
                dma_fence_put(fence);
        }
 err:
+       if (sync)
+               drm_syncobj_put(sync);
        drm_gem_object_unreference_unlocked(obj);
        return ret;
 }
diff --git a/include/drm/drm_syncobj.h b/include/drm/drm_syncobj.h
index 89976da542b1..9010ab8343e5 100644
--- a/include/drm/drm_syncobj.h
+++ b/include/drm/drm_syncobj.h
@@ -28,6 +28,8 @@
 
 #include "linux/dma-fence.h"
 
+struct drm_file;
+
 /**
  * struct drm_syncobj - sync object.
  *
diff --git a/include/uapi/drm/vgem_drm.h b/include/uapi/drm/vgem_drm.h
index bf66f5db6da8..94777197e561 100644
--- a/include/uapi/drm/vgem_drm.h
+++ b/include/uapi/drm/vgem_drm.h
@@ -46,8 +46,9 @@ struct drm_vgem_fence_attach {
        __u32 handle;
        __u32 flags;
 #define VGEM_FENCE_WRITE       0x1
+#define VGEM_FENCE_SYNCOBJ     0x2
        __u32 out_fence;
-       __u32 pad;
+       __u32 syncobj;
 };
 
 struct drm_vgem_fence_signal {
-- 
2.13.3

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