drm/i915: Introduce a ww transaction helper

Introduce a for_i915_gem_ww(){} utility to help make the code
around a ww transaction more readable.

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210617063018.92802-4-thomas.hellstrom@linux.intel.com

drivers/gpu/drm/i915/i915_gem_ww.h

@@ -11,11 +11,40 @@ struct i915_gem_ww_ctx {
 	struct ww_acquire_ctx ctx;
 	struct list_head obj_list;
 	struct drm_i915_gem_object *contended;
-	bool intr;
+	unsigned short intr;
+	unsigned short loop;
 };
 
 void i915_gem_ww_ctx_init(struct i915_gem_ww_ctx *ctx, bool intr);
 void i915_gem_ww_ctx_fini(struct i915_gem_ww_ctx *ctx);
 int __must_check i915_gem_ww_ctx_backoff(struct i915_gem_ww_ctx *ctx);
 void i915_gem_ww_unlock_single(struct drm_i915_gem_object *obj);
+
+/* Internal functions used by the inlines! Don't use. */
+static inline int __i915_gem_ww_fini(struct i915_gem_ww_ctx *ww, int err)
+{
+	ww->loop = 0;
+	if (err == -EDEADLK) {
+		err = i915_gem_ww_ctx_backoff(ww);
+		if (!err)
+			ww->loop = 1;
+	}
+
+	if (!ww->loop)
+		i915_gem_ww_ctx_fini(ww);
+
+	return err;
+}
+
+static inline void
+__i915_gem_ww_init(struct i915_gem_ww_ctx *ww, bool intr)
+{
+	i915_gem_ww_ctx_init(ww, intr);
+	ww->loop = 1;
+}
+
+#define for_i915_gem_ww(_ww, _err, _intr)			\
+	for (__i915_gem_ww_init(_ww, _intr); (_ww)->loop;	\
+	     _err = __i915_gem_ww_fini(_ww, _err))
+
 #endif