virtio-gpu api: multiple context types with explicit initialization

This feature allows for each virtio-gpu 3D context to be created
with a "context_init" variable.  This variable can specify:

 - the type of protocol used by the context via the capset id.
   This is useful for differentiating virgl, gfxstream, and venus
   protocols by host userspace.

 - other things in the future, such as the version of the context.

In addition, each different context needs one or more timelines, so
for example a virgl context's waiting can be independent on a
gfxstream context's waiting.

VIRTIO_GPU_FLAG_INFO_RING_IDX is introduced to specific to tell the
host which per-context command ring (or "hardware queue", distinct
from the virtio-queue) the fence should be associated with.

The new capability sets (gfxstream, venus etc.) are only defined in
the virtio-gpu spec and not defined in the header.
Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>
Acked-by: Lingfeng Yang <lfy@google.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20210921232024.817-2-gurchetansingh@chromium.orgSigned-off-by: Gerd Hoffmann <kraxel@redhat.com>

include/uapi/linux/virtio_gpu.h

@@ -59,6 +59,11 @@
  * VIRTIO_GPU_CMD_RESOURCE_CREATE_BLOB
  */
 #define VIRTIO_GPU_F_RESOURCE_BLOB       3
+/*
+ * VIRTIO_GPU_CMD_CREATE_CONTEXT with
+ * context_init and multiple timelines
+ */
+#define VIRTIO_GPU_F_CONTEXT_INIT        4
 
 enum virtio_gpu_ctrl_type {
 	VIRTIO_GPU_UNDEFINED = 0,
@@ -122,14 +127,20 @@ enum virtio_gpu_shm_id {
 	VIRTIO_GPU_SHM_ID_HOST_VISIBLE = 1
 };
 
-#define VIRTIO_GPU_FLAG_FENCE (1 << 0)
+#define VIRTIO_GPU_FLAG_FENCE         (1 << 0)
+/*
+ * If the following flag is set, then ring_idx contains the index
+ * of the command ring that needs to used when creating the fence
+ */
+#define VIRTIO_GPU_FLAG_INFO_RING_IDX (1 << 1)
 
 struct virtio_gpu_ctrl_hdr {
 	__le32 type;
 	__le32 flags;
 	__le64 fence_id;
 	__le32 ctx_id;
-	__le32 padding;
+	__u8 ring_idx;
+	__u8 padding[3];
 };
 
 /* data passed in the cursor vq */
@@ -269,10 +280,11 @@ struct virtio_gpu_resource_create_3d {
 };
 
 /* VIRTIO_GPU_CMD_CTX_CREATE */
+#define VIRTIO_GPU_CONTEXT_INIT_CAPSET_ID_MASK 0x000000ff
 struct virtio_gpu_ctx_create {
 	struct virtio_gpu_ctrl_hdr hdr;
 	__le32 nlen;
-	__le32 padding;
+	__le32 context_init;
 	char debug_name[64];
 };