backend/drm: steal CRTCs from disabled outputs

This commit allows outputs that need a CRTC to steal it from
user-disabled outputs. Note that in the case there are enough
CRTCs, disabled outputs don't loose it (so there's no modeset
and plane initialization needed after DPMS). CRTC allocation
still prefers to keep the old configuration, even if that means
allocating an extra CRTC to a disabled output.

CRTC reallocation now happen when enabling/disabling an output as
well as when trying to modeset. When enabling an output without a
CRTC, we realloc to try to steal a CRTC from a disabled output
(that doesn't really need the CRTC). When disabling an output, we
try to give our CRTC to an output that needs one. Modesetting is
similar to enabling.

A new DRM connector field has been added: `desired_enabled`.
Outputs without CRTCs get automatically disabled. This field keeps
track of the state desired by the user, allowing to automatically
re-enable outputs when a CRTC becomes free.

This required some changes to the allocation algorithm. Previously,
the algorithm tried to keep the previous configuration even if a
new configuration with a better score was possible (it only changed
configuration when the old one didn't work anymore). This is now
changed and the old configuration (still preferred) is only
retained without considering new possibilities when it's perfect
(all outputs have CRTCs).

User-disabled outputs now have `possible_crtcs` set to 0, meaning
they can only retain a previous CRTC (not acquire a new one). The
allocation algorithm has been updated to do not bump the score
when assigning a CRTC to a disabled output.

1 files changed, 14 insertions, 8 deletions

diff --git a/backend/drm/util.c b/backend/drm/util.c
index 050da2a6..f9637c33 100644
--- a/backend/drm/util.c
+++ b/backend/drm/util.c
@@ -223,7 +223,8 @@ struct match_state {
 static bool match_obj_(struct match_state *st, size_t skips, size_t score, size_t replaced, size_t i) {
 	// Finished
 	if (i >= st->num_res) {
-		if (score > st->score || (score == st->score && replaced < st->replaced)) {
+		if (score > st->score ||
+				(score == st->score && replaced < st->replaced)) {
 			st->score = score;
 			st->replaced = replaced;
 			memcpy(st->best, st->res, sizeof(st->best[0]) * st->num_res);
@@ -243,29 +244,33 @@ static bool match_obj_(struct match_state *st, size_t skips, size_t score, size_
 		return match_obj_(st, skips + 1, score, replaced, i + 1);
 	}
 
+	bool has_best = false;
+
 	/*
 	 * Attempt to use the current solution first, to try and avoid
 	 * recalculating everything
 	 */
 	if (st->orig[i] != UNMATCHED && !is_taken(i, st->res, st->orig[i])) {
 		st->res[i] = st->orig[i];
-		if (match_obj_(st, skips, score + 1, replaced, i + 1)) {
-			return true;
+		size_t obj_score = st->objs[st->res[i]] != 0 ? 1 : 0;
+		if (match_obj_(st, skips, score + obj_score, replaced, i + 1)) {
+			has_best = true;
 		}
 	}
 	if (st->orig[i] == UNMATCHED) {
 		st->res[i] = UNMATCHED;
-		match_obj_(st, skips, score, replaced, i + 1);
-		if (st->exit_early) {
-			return true;
+		if (match_obj_(st, skips, score, replaced, i + 1)) {
+			has_best = true;
 		}
 	}
+	if (st->exit_early) {
+		return true;
+	}
 
 	if (st->orig[i] != UNMATCHED) {
 		++replaced;
 	}
 
-	bool has_best = false;
 	for (size_t candidate = 0; candidate < st->num_objs; ++candidate) {
 		// We tried this earlier
 		if (candidate == st->orig[i]) {
@@ -283,7 +288,8 @@ static bool match_obj_(struct match_state *st, size_t skips, size_t score, size_
 		}
 
 		st->res[i] = candidate;
-		if (match_obj_(st, skips, score + 1, replaced, i + 1)) {
+		size_t obj_score = st->objs[candidate] != 0 ? 1 : 0;
+		if (match_obj_(st, skips, score + obj_score, replaced, i + 1)) {
 			has_best = true;
 		}