drm/vmwgfx: fix all kernel-doc warnings in stdu

kernel test robot reports one kernel-doc warning in stdu, but
running scripts/kernel-doc in -Wall mode reports several more,
so fix all of them at one time:

vmwgfx_stdu.c:76: warning: Excess struct member 'transfer' description in 'vmw_stdu_dirty'
vmwgfx_stdu.c:103: warning: missing initial short description on line:
 * struct vmw_screen_target_display_unit
vmwgfx_stdu.c:215: warning: No description found for return value of 'vmw_stdu_bind_st'
vmwgfx_stdu.c:320: warning: No description found for return value of 'vmw_stdu_destroy_st'
vmwgfx_stdu.c:551: warning: No description found for return value of 'vmw_kms_stdu_readback'
vmwgfx_stdu.c:719: warning: No description found for return value of 'vmw_kms_stdu_surface_dirty'
vmwgfx_stdu.c:895: warning: No description found for return value of 'vmw_stdu_primary_plane_prepare_fb'
vmwgfx_stdu.c:1470: warning: No description found for return value of 'vmw_stdu_init'
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202312150347.5icezNlK-lkp@intel.com/
Cc: Zack Rusin <zackr@vmware.com>
Cc: VMware Graphics Reviewers <linux-graphics-maintainer@vmware.com>
Cc: dri-devel@lists.freedesktop.org
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Zack Rusin <zack.rusin@broadcom.com>
Signed-off-by: Zack Rusin <zack.rusin@broadcom.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231215234102.16574-1-rdunlap@infradead.org

drivers/gpu/drm/vmwgfx/vmwgfx_stdu.c

@@ -53,7 +53,6 @@ enum stdu_content_type {
  * struct vmw_stdu_dirty - closure structure for the update functions
  *
  * @base: The base type we derive from. Used by vmw_kms_helper_dirty().
- * @transfer: Transfer direction for DMA command.
  * @left: Left side of bounding box.
  * @right: Right side of bounding box.
  * @top: Top side of bounding box.
@@ -100,7 +99,7 @@ struct vmw_stdu_update_gb_image {
 };
 
 /**
- * struct vmw_screen_target_display_unit
+ * struct vmw_screen_target_display_unit - conglomerated STDU structure
  *
  * @base: VMW specific DU structure
  * @display_srf: surface to be displayed.  The dimension of this will always
@@ -208,6 +207,8 @@ static int vmw_stdu_define_st(struct vmw_private *dev_priv,
  * @res: Buffer to bind to the screen target.  Set to NULL to blank screen.
  *
  * Binding a surface to a Screen Target the same as flipping
+ *
+ * Returns: %0 on success or -errno code on failure
  */
 static int vmw_stdu_bind_st(struct vmw_private *dev_priv,
 			    struct vmw_screen_target_display_unit *stdu,
@@ -314,6 +315,9 @@ static int vmw_stdu_update_st(struct vmw_private *dev_priv,
  *
  * @dev_priv:  VMW DRM device
  * @stdu: display unit to destroy
+ *
+ * Returns: %0 on success, negative error code on failure. -ERESTARTSYS if
+ * interrupted.
  */
 static int vmw_stdu_destroy_st(struct vmw_private *dev_priv,
 			       struct vmw_screen_target_display_unit *stdu)
@@ -536,7 +540,8 @@ static void vmw_stdu_bo_cpu_commit(struct vmw_kms_dirty *dirty)
  * If DMA-ing till the screen target system, the function will also notify
  * the screen target system that a bounding box of the cliprects has been
  * updated.
- * Returns 0 on success, negative error code on failure. -ERESTARTSYS if
+ *
+ * Returns: %0 on success, negative error code on failure. -ERESTARTSYS if
  * interrupted.
  */
 int vmw_kms_stdu_readback(struct vmw_private *dev_priv,
@@ -703,7 +708,7 @@ static void vmw_kms_stdu_surface_fifo_commit(struct vmw_kms_dirty *dirty)
  * case the device has already synchronized.
  * @crtc: If crtc is passed, perform surface dirty on that crtc only.
  *
- * Returns 0 on success, negative error code on failure. -ERESTARTSYS if
+ * Returns: %0 on success, negative error code on failure. -ERESTARTSYS if
  * interrupted.
  */
 int vmw_kms_stdu_surface_dirty(struct vmw_private *dev_priv,
@@ -887,7 +892,7 @@ vmw_stdu_primary_plane_cleanup_fb(struct drm_plane *plane,
  * backed by a buffer object.  The display surface is pinned here, and it'll
  * be unpinned in .cleanup_fb()
  *
- * Returns 0 on success
+ * Returns: %0 on success
  */
 static int
 vmw_stdu_primary_plane_prepare_fb(struct drm_plane *plane,
@@ -1465,6 +1470,8 @@ static const struct drm_crtc_helper_funcs vmw_stdu_crtc_helper_funcs = {
  * This function is called once per CRTC, and allocates one Screen Target
  * display unit to represent that CRTC.  Since the SVGA device does not separate
  * out encoder and connector, they are represented as part of the STDU as well.
+ *
+ * Returns: %0 on success or -errno code on failure
  */
 static int vmw_stdu_init(struct vmw_private *dev_priv, unsigned unit)
 {