drm: Add additional atomic helpers for shadow-buffered planes

Several drivers use GEM buffer objects as shadow buffers for the actual
framebuffer memory. Right now, drivers do these vmap operations in their
commit tail, which is actually not allowed by the locking rules for
the dma-buf reservation lock. The involved BO has to be vmapped in the
plane's prepare_fb callback and vunmapped in cleanup_fb.

This patch introduces atomic helpers for such shadow planes. Plane
functions manage the plane state for shadow planes. The provided
implementations for prepare_fb and cleanup_fb vmap and vunmap all BOs of
struct drm_plane_state.fb. The mappings are afterwards available in the
plane's commit-tail functions.

For now, all rsp drivers use the simple KMS helpers, so we add the plane
callbacks and wrappers for simple KMS. The internal plane functions can
later be exported as needed.

v3:
	* documentation fixes
v2:
	* make duplicate_state interface compatible with
	  struct drm_plane_funcs

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Tested-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210208115538.6430-4-tzimmermann@suse.de

1 files changed, 73 insertions, 0 deletions

diff --git a/include/drm/drm_gem_atomic_helper.h b/include/drm/drm_gem_atomic_helper.h
new file mode 100644
index 000000000000..08b96ccea325
--- /dev/null
+++ b/include/drm/drm_gem_atomic_helper.h
@@ -0,0 +1,73 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#ifndef __DRM_GEM_ATOMIC_HELPER_H__
+#define __DRM_GEM_ATOMIC_HELPER_H__
+
+#include <linux/dma-buf-map.h>
+
+#include <drm/drm_plane.h>
+
+struct drm_simple_display_pipe;
+
+/*
+ * Helpers for planes with shadow buffers
+ */
+
+/**
+ * struct drm_shadow_plane_state - plane state for planes with shadow buffers
+ *
+ * For planes that use a shadow buffer, struct drm_shadow_plane_state
+ * provides the regular plane state plus mappings of the shadow buffer
+ * into kernel address space.
+ */
+struct drm_shadow_plane_state {
+	/** @base: plane state */
+	struct drm_plane_state base;
+
+	/* Transitional state - do not export or duplicate */
+
+	/**
+	 * @map: Mappings of the plane's framebuffer BOs in to kernel address space
+	 *
+	 * The memory mappings stored in map should be established in the plane's
+	 * prepare_fb callback and removed in the cleanup_fb callback.
+	 */
+	struct dma_buf_map map[4];
+};
+
+/**
+ * to_drm_shadow_plane_state - upcasts from struct drm_plane_state
+ * @state: the plane state
+ */
+static inline struct drm_shadow_plane_state *
+to_drm_shadow_plane_state(struct drm_plane_state *state)
+{
+	return container_of(state, struct drm_shadow_plane_state, base);
+}
+
+int drm_gem_simple_kms_prepare_shadow_fb(struct drm_simple_display_pipe *pipe,
+					 struct drm_plane_state *plane_state);
+void drm_gem_simple_kms_cleanup_shadow_fb(struct drm_simple_display_pipe *pipe,
+					  struct drm_plane_state *plane_state);
+void drm_gem_simple_kms_reset_shadow_plane(struct drm_simple_display_pipe *pipe);
+struct drm_plane_state *
+drm_gem_simple_kms_duplicate_shadow_plane_state(struct drm_simple_display_pipe *pipe);
+void drm_gem_simple_kms_destroy_shadow_plane_state(struct drm_simple_display_pipe *pipe,
+						   struct drm_plane_state *plane_state);
+
+/**
+ * DRM_GEM_SIMPLE_DISPLAY_PIPE_SHADOW_PLANE_FUNCS -
+ *	Initializes struct drm_simple_display_pipe_funcs for shadow-buffered planes
+ *
+ * Drivers may use GEM BOs as shadow buffers over the framebuffer memory. This
+ * macro initializes struct drm_simple_display_pipe_funcs to use the rsp helper
+ * functions.
+ */
+#define DRM_GEM_SIMPLE_DISPLAY_PIPE_SHADOW_PLANE_FUNCS \
+	.prepare_fb = drm_gem_simple_kms_prepare_shadow_fb, \
+	.cleanup_fb = drm_gem_simple_kms_cleanup_shadow_fb, \
+	.reset_plane = drm_gem_simple_kms_reset_shadow_plane, \
+	.duplicate_plane_state = drm_gem_simple_kms_duplicate_shadow_plane_state, \
+	.destroy_plane_state = drm_gem_simple_kms_destroy_shadow_plane_state
+
+#endif /* __DRM_GEM_ATOMIC_HELPER_H__ */