drm/i915: Clean-up outdated struct_mutex comments

The struct_mutex will be removed from the DRM subsystem, as it was a
legacy BKL that was only used by i915 driver. After review, it was
concluded that its usage was no longer necessary

This patch updates various comments in the i915 codebase to
either remove or clarify references to struct_mutex, in order to
prevent future misunderstandings.

* i915_drv.h: Removed the statement that stolen_lock is the inner lock
  when overlaps with struct_mutex, since struct_mutex is no longer used
  in the driver.
* i915_gem.c: Removed parentheses suggesting usage of struct_mutex, which
  which is no longer used.

Signed-off-by: Luiz Otavio Mello <[email protected]>
Reviewed-by: Rodrigo Vivi <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Rodrigo Vivi <[email protected]>

Author: LuizOt31

drivers/gpu/drm/i915/i915_drv.h

@@ -116,8 +116,7 @@ struct i915_gem_mm {
 	struct intel_memory_region *stolen_region;
 	/** Memory allocator for GTT stolen memory */
 	struct drm_mm stolen;
-	/** Protects the usage of the GTT stolen memory allocator. This is
-	 * always the inner lock when overlapping with struct_mutex. */
+	/** Protects the usage of the GTT stolen memory allocator */
 	struct mutex stolen_lock;
 
 	/* Protects bound_list/unbound_list and #drm_i915_gem_object.mm.link */

drivers/gpu/drm/i915/i915_gem.c

@@ -847,8 +847,7 @@ void i915_gem_runtime_suspend(struct drm_i915_private *i915)
 	/*
 	 * Only called during RPM suspend. All users of the userfault_list
 	 * must be holding an RPM wakeref to ensure that this can not
-	 * run concurrently with themselves (and use the struct_mutex for
-	 * protection between themselves).
+	 * run concurrently with themselves.
 	 */
 
 	list_for_each_entry_safe(obj, on,