drm: add parameter explanation for some gem dmabuf_ops

To reduce some warnings.
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Samuel Li <Samuel.Li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1522092145-12645-1-git-send-email-Samuel.Li@amd.com

drivers/gpu/drm/drm_prime.c

@@ -331,6 +331,9 @@ EXPORT_SYMBOL(drm_gem_map_dma_buf);
 
 /**
  * drm_gem_unmap_dma_buf - unmap_dma_buf implementation for GEM
+ * @attach: attachment to unmap buffer from
+ * @sgt: scatterlist info of the buffer to unmap
+ * @dir: direction of DMA transfer
  *
  * Not implemented. The unmap is done at drm_gem_map_detach().  This can be
  * used as the &dma_buf_ops.unmap_dma_buf callback.
@@ -429,6 +432,8 @@ EXPORT_SYMBOL(drm_gem_dmabuf_vunmap);
 
 /**
  * drm_gem_dmabuf_kmap_atomic - map_atomic implementation for GEM
+ * @dma_buf: buffer to be mapped
+ * @page_num: page number within the buffer
  *
  * Not implemented. This can be used as the &dma_buf_ops.map_atomic callback.
  */
@@ -441,6 +446,9 @@ EXPORT_SYMBOL(drm_gem_dmabuf_kmap_atomic);
 
 /**
  * drm_gem_dmabuf_kunmap_atomic - unmap_atomic implementation for GEM
+ * @dma_buf: buffer to be unmapped
+ * @page_num: page number within the buffer
+ * @addr: virtual address of the buffer
  *
  * Not implemented. This can be used as the &dma_buf_ops.unmap_atomic callback.
  */
@@ -453,6 +461,8 @@ EXPORT_SYMBOL(drm_gem_dmabuf_kunmap_atomic);
 
 /**
  * drm_gem_dmabuf_kmap - map implementation for GEM
+ * @dma_buf: buffer to be mapped
+ * @page_num: page number within the buffer
  *
  * Not implemented. This can be used as the &dma_buf_ops.map callback.
  */
@@ -464,6 +474,9 @@ EXPORT_SYMBOL(drm_gem_dmabuf_kmap);
 
 /**
  * drm_gem_dmabuf_kunmap - unmap implementation for GEM
+ * @dma_buf: buffer to be unmapped
+ * @page_num: page number within the buffer
+ * @addr: virtual address of the buffer
  *
  * Not implemented. This can be used as the &dma_buf_ops.unmap callback.
  */