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, 7 insertions, 2 deletions

diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c
index 7b4ad05fe1c0..3cc5fbd78ee2 100644
--- a/drivers/gpu/drm/drm_mm.c
+++ b/drivers/gpu/drm/drm_mm.c
@@ -480,6 +480,7 @@ int drm_mm_insert_node_in_range(struct drm_mm * const mm,
 {
 	struct drm_mm_node *hole;
 	u64 remainder_mask;
+	bool once;
 
 	DRM_MM_BUG_ON(range_start >= range_end);
 
@@ -492,9 +493,13 @@ int drm_mm_insert_node_in_range(struct drm_mm * const mm,
 	if (alignment <= 1)
 		alignment = 0;
 
+	once = mode & DRM_MM_INSERT_ONCE;
+	mode &= ~DRM_MM_INSERT_ONCE;
+
 	remainder_mask = is_power_of_2(alignment) ? alignment - 1 : 0;
-	for (hole = first_hole(mm, range_start, range_end, size, mode); hole;
-	     hole = next_hole(mm, hole, mode)) {
+	for (hole = first_hole(mm, range_start, range_end, size, mode);
+	     hole;
+	     hole = once ? NULL : next_hole(mm, hole, mode)) {
 		u64 hole_start = __drm_mm_hole_node_start(hole);
 		u64 hole_end = hole_start + hole->hole_size;
 		u64 adj_start, adj_end;