drm/mm: Add a search-by-address variant to only inspect a single hole

Searching for an available hole by address is slow, as there no
guarantee that a hole will be available and so we must walk over all
nodes in the rbtree before we determine the search was futile. In many
cases, the caller doesn't strictly care for the highest available hole
and was just opportunistically laying out the address space in a
preferred order. In such cases, the caller can accept any address and
would rather do so then do a slow walk.

To be able to mix search strategies, the caller wants to tell the drm_mm
how long to spend on the search. Without a good guide for what should be
the best split, start with a request to try once at most. That is return
the top-most (or lowest) hole if it fulfils the alignment and size
requirements.

v2: Documentation, by why of example (selftests) and kerneldoc.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180521082131.13744-2-chris@chris-wilson.co.uk

1 files changed, 32 insertions, 0 deletions

diff --git a/include/drm/drm_mm.h b/include/drm/drm_mm.h
index e3aa3bfd4860..2c3bbb43c7d1 100644
--- a/include/drm/drm_mm.h
+++ b/include/drm/drm_mm.h
@@ -109,6 +109,38 @@ enum drm_mm_insert_mode {
 	 * Allocates the node from the bottom of the found hole.
 	 */
 	DRM_MM_INSERT_EVICT,
+
+	/**
+	 * @DRM_MM_INSERT_ONCE:
+	 *
+	 * Only check the first hole for suitablity and report -ENOSPC
+	 * immediately otherwise, rather than check every hole until a
+	 * suitable one is found. Can only be used in conjunction with another
+	 * search method such as DRM_MM_INSERT_HIGH or DRM_MM_INSERT_LOW.
+	 */
+	DRM_MM_INSERT_ONCE = BIT(31),
+
+	/**
+	 * @DRM_MM_INSERT_HIGHEST:
+	 *
+	 * Only check the highest hole (the hole with the largest address) and
+	 * insert the node at the top of the hole or report -ENOSPC if
+	 * unsuitable.
+	 *
+	 * Does not search all holes.
+	 */
+	DRM_MM_INSERT_HIGHEST = DRM_MM_INSERT_HIGH | DRM_MM_INSERT_ONCE,
+
+	/**
+	 * @DRM_MM_INSERT_LOWEST:
+	 *
+	 * Only check the lowest hole (the hole with the smallest address) and
+	 * insert the node at the bottom of the hole or report -ENOSPC if
+	 * unsuitable.
+	 *
+	 * Does not search all holes.
+	 */
+	DRM_MM_INSERT_LOWEST  = DRM_MM_INSERT_LOW | DRM_MM_INSERT_ONCE,
 };
 
 /**