From a055f23b3b116b1b8bbf6e862b9f1c93aac86455 Mon Sep 17 00:00:00 2001
From: Daniel Playfair Cal <daniel.playfair.cal@gmail.com>
Date: Sun, 10 Jan 2021 14:46:16 +1100
Subject: [PATCH] backend/drm: keep removed modes allocated if they are in use

After a fixed mode is removed from an output, it remains the current or
pending mode for an output until the compositor requests a different
mode. This change ensures that removed modes are not freed until the
compositor has had the opportunity to know that the mode was removed,
and in the case of the current or pending mode, that the mode is no
longer the current or pending mode.
---
 backend/drm/drm.c  |  8 +++++++-
 types/wlr_output.c | 45 +++++++++++++++++++++++++++++++++++++++------
 2 files changed, 46 insertions(+), 7 deletions(-)

diff --git a/backend/drm/drm.c b/backend/drm/drm.c
index 3ff20b796..c040d0798 100644
--- a/backend/drm/drm.c
+++ b/backend/drm/drm.c
@@ -1255,7 +1255,13 @@ static bool update_modes(drmModeConnector *drm_conn,
 			previous_drm_mode->wlr_mode.preferred ? "(preferred)" : "");
 
 		wl_list_remove(&previous_drm_mode->wlr_mode.link);
-		free(previous_drm_mode);
+
+		// Free the removed mode unless it is the current or pending mode
+		if (previous_mode != wlr_conn->output.current_mode &&
+				!(wlr_conn->output.pending.committed & WLR_OUTPUT_STATE_MODE &&
+				previous_mode != wlr_conn->output.pending.mode)) {
+			free(previous_drm_mode);
+		}
 	}
 
 	if (drm_conn->count_modes > wl_list_length(&wlr_conn->output.modes)) {
diff --git a/types/wlr_output.c b/types/wlr_output.c
index 1cb594cb0..d200ac8ac 100644
--- a/types/wlr_output.c
+++ b/types/wlr_output.c
@@ -154,19 +154,47 @@ void wlr_output_enable(struct wlr_output *output, bool enable) {
 	output->pending.enabled = enable;
 }
 
-static void output_state_clear_mode(struct wlr_output_state *state) {
-	if (!(state->committed & WLR_OUTPUT_STATE_MODE)) {
+static void wlr_output_free_mode_if_not_used(struct wlr_output *output,
+		struct wlr_output_mode *mode) {
+	if (output->current_mode == mode) {
 		return;
 	}
 
-	state->mode = NULL;
+	if (output->pending.committed & WLR_OUTPUT_STATE_MODE
+			&& output->pending.mode == mode) {
+		return;
+	}
 
-	state->committed &= ~WLR_OUTPUT_STATE_MODE;
+	struct wlr_output_mode *available_mode;
+	bool found = false;
+	wl_list_for_each(available_mode, &output->modes, link) {
+		if (available_mode == mode) {
+			found = true;
+			break;
+		}
+	}
+	if (!found) {
+		free(mode);
+	}
+}
+
+static void output_state_clear_mode(struct wlr_output *output) {
+	if (!(output->pending.committed & WLR_OUTPUT_STATE_MODE)) {
+		return;
+	}
+
+	struct wlr_output_mode *old_mode = output->pending.mode;
+
+	output->pending.mode = NULL;
+
+	output->pending.committed &= ~WLR_OUTPUT_STATE_MODE;
+
+	wlr_output_free_mode_if_not_used(output, old_mode);
 }
 
 void wlr_output_set_mode(struct wlr_output *output,
 		struct wlr_output_mode *mode) {
-	output_state_clear_mode(&output->pending);
+	output_state_clear_mode(output);
 
 	if (output->current_mode == mode) {
 		return;
@@ -179,7 +207,7 @@ void wlr_output_set_mode(struct wlr_output *output,
 
 void wlr_output_set_custom_mode(struct wlr_output *output, int32_t width,
 		int32_t height, int32_t refresh) {
-	output_state_clear_mode(&output->pending);
+	output_state_clear_mode(output);
 
 	if (output->width == width && output->height == height &&
 			output->refresh == refresh) {
@@ -195,13 +223,18 @@ void wlr_output_set_custom_mode(struct wlr_output *output, int32_t width,
 
 void wlr_output_update_mode(struct wlr_output *output,
 		struct wlr_output_mode *mode) {
+	struct wlr_output_mode *old_mode = output->current_mode;
+
 	output->current_mode = mode;
+
 	if (mode != NULL) {
 		wlr_output_update_custom_mode(output, mode->width, mode->height,
 			mode->refresh);
 	} else {
 		wlr_output_update_custom_mode(output, 0, 0, 0);
 	}
+
+	wlr_output_free_mode_if_not_used(output, old_mode);
 }
 
 void wlr_output_update_custom_mode(struct wlr_output *output, int32_t width,