spu_wbox_write
if (!spu_wbox_write(ctx, wbox_data)) {
count = spufs_wait(ctx->wbox_wq, spu_wbox_write(ctx, wbox_data));
ret = spu_wbox_write(ctx, wbox_data);
size_t spu_wbox_write(struct spu_context *ctx, u32 data);