drm/i915: Trim unused workaround list entries

The new workaround list allocator grows the list in chunks so will end up
with some unused space. Trim it when the initialization phase is done to
free up a tiny bit of slab.

v2:
 * Simplify with kmemdup. (Chris Wilson)

v3:
 * Refactor for __size removal.
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20181203125014.3219-8-tvrtko.ursulin@linux.intel.com

drivers/gpu/drm/i915/intel_workarounds.c

@@ -53,8 +53,22 @@ static void wa_init_start(struct i915_wa_list *wal, const char *name)
 	wal->name = name;
 }
 
+#define WA_LIST_CHUNK (1 << 4)
+
 static void wa_init_finish(struct i915_wa_list *wal)
 {
+	/* Trim unused entries. */
+	if (!IS_ALIGNED(wal->count, WA_LIST_CHUNK)) {
+		struct i915_wa *list = kmemdup(wal->list,
+					       wal->count * sizeof(*list),
+					       GFP_KERNEL);
+
+		if (list) {
+			kfree(wal->list);
+			wal->list = list;
+		}
+	}
+
 	if (!wal->count)
 		return;
 
@@ -66,7 +80,7 @@ static void _wa_add(struct i915_wa_list *wal, const struct i915_wa *wa)
 {
 	unsigned int addr = i915_mmio_reg_offset(wa->reg);
 	unsigned int start = 0, end = wal->count;
-	const unsigned int grow = 1 << 4;
+	const unsigned int grow = WA_LIST_CHUNK;
 	struct i915_wa *wa_;
 
 	GEM_BUG_ON(!is_power_of_2(grow));