[PATCH 2/3] drm/i915/display: Add infra to reduce global state funcs boilerplate

[Gustavo Sousa <gustavo.sousa@xxxxxxxxx>]

If we look at how the members of struct intel_global_state_funcs, we see
a common pattern repeating itself. Let's add the necessary
infra-structure to allow reducing the boilerplate. We do that by
adding common generic implementations for each member and adding a macro
INTEL_GLOBAL_STATE_DEFAULTS() to be used when initializing an instance
of struct intel_global_state_funcs.

That way, a global state that does not need custom behavior can have
its funcs structure be initialized as in the following example,

    static const struct intel_global_state_funcs <prefix>_funcs = {
           INTEL_GLOBAL_STATE_DEFAULTS(struct <prefix>_state, <base_member_name>),
    };

, without the need to implementing the functions.

That doesn't come without cost - we will need to store two size_t
members -, but that cost is arguably justified by the simplification
gained.

In an upcoming change we will put that infra into action on existing
users.

Signed-off-by: Gustavo Sousa <gustavo.sousa@xxxxxxxxx>
---
 .../gpu/drm/i915/display/intel_global_state.c | 41 ++++++++++++++++++-
 .../gpu/drm/i915/display/intel_global_state.h | 15 +++++++
 2 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_global_state.c b/drivers/gpu/drm/i915/display/intel_global_state.c
index cbcd1e91b7be..4b4c33fa99fb 100644
--- a/drivers/gpu/drm/i915/display/intel_global_state.c
+++ b/drivers/gpu/drm/i915/display/intel_global_state.c
@@ -59,7 +59,10 @@ static void __intel_atomic_global_state_free(struct kref *kref)
 
 	commit_put(obj_state->commit);
 
-	obj->funcs->atomic_destroy_state(obj, obj_state);
+	if (obj->funcs->atomic_destroy_state)
+		obj->funcs->atomic_destroy_state(obj, obj_state);
+	else
+		intel_atomic_global_destroy_state_common(obj, obj_state);
 }
 
 static void intel_atomic_global_state_put(struct intel_global_state *obj_state)
@@ -164,7 +167,11 @@ intel_atomic_get_global_obj_state(struct intel_atomic_state *state,
 	index = state->num_global_objs;
 	memset(&state->global_objs[index], 0, sizeof(*state->global_objs));
 
-	obj_state = obj->funcs->atomic_duplicate_state(obj);
+	if (obj->funcs->atomic_duplicate_state)
+		obj_state = obj->funcs->atomic_duplicate_state(obj);
+	else
+		obj_state = intel_atomic_global_duplicate_state_common(obj);
+
 	if (!obj_state)
 		return ERR_PTR(-ENOMEM);
 
@@ -382,3 +389,33 @@ intel_atomic_global_state_commit_done(struct intel_atomic_state *state)
 		complete_all(&commit->done);
 	}
 }
+
+struct intel_global_state *
+intel_atomic_global_duplicate_state_common(struct intel_global_obj *obj)
+{
+	void *state_wrapper;
+
+	if (WARN_ON(obj->funcs->state_size == 0))
+		return NULL;
+
+	state_wrapper = (void *)obj->state - obj->funcs->base_offset;
+
+	state_wrapper = kmemdup(state_wrapper, obj->funcs->state_size, GFP_KERNEL);
+	if (!state_wrapper)
+		return NULL;
+
+	return state_wrapper + obj->funcs->base_offset;
+}
+
+void intel_atomic_global_destroy_state_common(struct intel_global_obj *obj,
+					      struct intel_global_state *state)
+{
+	void *state_wrapper;
+
+	if (WARN_ON(obj->funcs->state_size == 0))
+		return;
+
+	state_wrapper = (void *)state - obj->funcs->base_offset;
+
+	kfree(state_wrapper);
+}
diff --git a/drivers/gpu/drm/i915/display/intel_global_state.h b/drivers/gpu/drm/i915/display/intel_global_state.h
index 6506a8e32972..e47e007225cc 100644
--- a/drivers/gpu/drm/i915/display/intel_global_state.h
+++ b/drivers/gpu/drm/i915/display/intel_global_state.h
@@ -8,6 +8,8 @@
 
 #include <linux/kref.h>
 #include <linux/list.h>
+#include <linux/stddef.h>
+#include <linux/types.h>
 
 struct drm_i915_private;
 struct intel_atomic_state;
@@ -15,6 +17,10 @@ struct intel_global_obj;
 struct intel_global_state;
 
 struct intel_global_state_funcs {
+	/* state_size and base_offset are initialized by INTEL_GLOBAL_STATE_DEFAULTS() */
+	size_t state_size;
+	size_t base_offset;
+
 	struct intel_global_state *(*atomic_duplicate_state)(struct intel_global_obj *obj);
 	void (*atomic_destroy_state)(struct intel_global_obj *obj,
 				     struct intel_global_state *state);
@@ -26,6 +32,10 @@ struct intel_global_obj {
 	const struct intel_global_state_funcs *funcs;
 };
 
+#define INTEL_GLOBAL_STATE_DEFAULTS(type, base_member) \
+	.state_size = sizeof(type), \
+	.base_offset = offsetof(type, base_member)
+
 #define intel_for_each_global_obj(obj, dev_priv) \
 	list_for_each_entry(obj, &(dev_priv)->display.global.obj_list, head)
 
@@ -96,4 +106,9 @@ int intel_atomic_global_state_wait_for_dependencies(struct intel_atomic_state *s
 
 bool intel_atomic_global_state_is_serialized(struct intel_atomic_state *state);
 
+struct intel_global_state *
+intel_atomic_global_duplicate_state_common(struct intel_global_obj *obj);
+void intel_atomic_global_destroy_state_common(struct intel_global_obj *obj,
+					      struct intel_global_state *state);
+
 #endif
-- 
2.47.1