drm/i915: add a helper to free the members of i915_params

Abstract the one user in anticipation of more. Set the dangling pointers
to NULL while at it.
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/8637d1e5049dc003718772f19d664aeaf9540856.1545920737.git.jani.nikula@intel.com

drivers/gpu/drm/i915/i915_gpu_error.c

@@ -963,17 +963,10 @@ static void i915_error_object_free(struct drm_i915_error_object *obj)
 	kfree(obj);
 }
 
-static __always_inline void free_param(const char *type, void *x)
-{
-	if (!__builtin_strcmp(type, "char *"))
-		kfree(*(void **)x);
-}
 
 static void cleanup_params(struct i915_gpu_state *error)
 {
-#define FREE(T, x, ...) free_param(#T, &error->params.x);
-	I915_PARAMS_FOR_EACH(FREE);
-#undef FREE
+	i915_params_free(&error->params);
 }
 
 static void cleanup_uc_state(struct i915_gpu_state *error)

drivers/gpu/drm/i915/i915_params.c

@@ -217,3 +217,19 @@ void i915_params_copy(struct i915_params *dest, const struct i915_params *src)
 	I915_PARAMS_FOR_EACH(DUP);
 #undef DUP
 }
+
+static __always_inline void free_param(const char *type, void *x)
+{
+	if (!__builtin_strcmp(type, "char *")) {
+		kfree(*(void **)x);
+		*(void **)x = NULL;
+	}
+}
+
+/* free the allocated members, *not* the passed in params itself */
+void i915_params_free(struct i915_params *params)
+{
+#define FREE(T, x, ...) free_param(#T, &params->x);
+	I915_PARAMS_FOR_EACH(FREE);
+#undef FREE
+}

drivers/gpu/drm/i915/i915_params.h

@@ -79,6 +79,7 @@ extern struct i915_params i915_modparams __read_mostly;
 
 void i915_params_dump(const struct i915_params *params, struct drm_printer *p);
 void i915_params_copy(struct i915_params *dest, const struct i915_params *src);
+void i915_params_free(struct i915_params *params);
 
 #endif