drm/fb-helper: Fix vt restore

From Daniel Vetter
7b6902118146835fa67b52f624576d30b1c9e09f in linux 5.7.y/5.7.7
dc5bdb68b5b369d5bc7d1de96fa64cc1737a6320 in mainline linux

1 files changed, 57 insertions, 18 deletions

diff --git a/sys/dev/pci/drm/drm_fb_helper.c b/sys/dev/pci/drm/drm_fb_helper.c
index 3763157e8b3..6ddad45c990 100644
--- a/sys/dev/pci/drm/drm_fb_helper.c
+++ b/sys/dev/pci/drm/drm_fb_helper.c
@@ -229,18 +229,9 @@ int drm_fb_helper_debug_leave(struct fb_info *info)
 }
 EXPORT_SYMBOL(drm_fb_helper_debug_leave);
 
-/**
- * drm_fb_helper_restore_fbdev_mode_unlocked - restore fbdev configuration
- * @fb_helper: driver-allocated fbdev helper, can be NULL
- *
- * This should be called from driver's drm &drm_driver.lastclose callback
- * when implementing an fbcon on top of kms using this helper. This ensures that
- * the user isn't greeted with a black screen when e.g. X dies.
- *
- * RETURNS:
- * Zero if everything went ok, negative error code otherwise.
- */
-int drm_fb_helper_restore_fbdev_mode_unlocked(struct drm_fb_helper *fb_helper)
+static int
+__drm_fb_helper_restore_fbdev_mode_unlocked(struct drm_fb_helper *fb_helper,
+					    bool force)
 {
 	bool do_delayed;
 	int ret;
@@ -251,13 +242,22 @@ int drm_fb_helper_restore_fbdev_mode_unlocked(struct drm_fb_helper *fb_helper)
 	if (READ_ONCE(fb_helper->deferred_setup))
 		return 0;
 
-	mutex_lock(&fb_helper->lock);
-#ifdef __linux__
-	ret = drm_client_modeset_commit(&fb_helper->client);
-#else
-	ret = drm_client_modeset_commit_locked(&fb_helper->client);
+#ifdef __OpenBSD__
+	force = true;
 #endif
 
+	mutex_lock(&fb_helper->lock);
+	if (force) {
+		/*
+		 * Yes this is the _locked version which expects the master lock
+		 * to be held. But for forced restores we're intentionally
+		 * racing here, see drm_fb_helper_set_par().
+		 */
+		ret = drm_client_modeset_commit_locked(&fb_helper->client);
+	} else {
+		ret = drm_client_modeset_commit(&fb_helper->client);
+	}
+
 	do_delayed = fb_helper->delayed_hotplug;
 	if (do_delayed)
 		fb_helper->delayed_hotplug = false;
@@ -268,6 +268,22 @@ int drm_fb_helper_restore_fbdev_mode_unlocked(struct drm_fb_helper *fb_helper)
 
 	return ret;
 }
+
+/**
+ * drm_fb_helper_restore_fbdev_mode_unlocked - restore fbdev configuration
+ * @fb_helper: driver-allocated fbdev helper, can be NULL
+ *
+ * This should be called from driver's drm &drm_driver.lastclose callback
+ * when implementing an fbcon on top of kms using this helper. This ensures that
+ * the user isn't greeted with a black screen when e.g. X dies.
+ *
+ * RETURNS:
+ * Zero if everything went ok, negative error code otherwise.
+ */
+int drm_fb_helper_restore_fbdev_mode_unlocked(struct drm_fb_helper *fb_helper)
+{
+	return __drm_fb_helper_restore_fbdev_mode_unlocked(fb_helper, false);
+}
 EXPORT_SYMBOL(drm_fb_helper_restore_fbdev_mode_unlocked);
 
 #ifdef CONFIG_MAGIC_SYSRQ
@@ -1334,6 +1350,7 @@ int drm_fb_helper_set_par(struct fb_info *info)
 {
 	struct drm_fb_helper *fb_helper = info->par;
 	struct fb_var_screeninfo *var = &info->var;
+	bool force;
 
 	if (oops_in_progress)
 		return -EBUSY;
@@ -1343,7 +1360,29 @@ int drm_fb_helper_set_par(struct fb_info *info)
 		return -EINVAL;
 	}
 
-	drm_fb_helper_restore_fbdev_mode_unlocked(fb_helper);
+	/*
+	 * Normally we want to make sure that a kms master takes precedence over
+	 * fbdev, to avoid fbdev flickering and occasionally stealing the
+	 * display status. But Xorg first sets the vt back to text mode using
+	 * the KDSET IOCTL with KD_TEXT, and only after that drops the master
+	 * status when exiting.
+	 *
+	 * In the past this was caught by drm_fb_helper_lastclose(), but on
+	 * modern systems where logind always keeps a drm fd open to orchestrate
+	 * the vt switching, this doesn't work.
+	 *
+	 * To not break the userspace ABI we have this special case here, which
+	 * is only used for the above case. Everything else uses the normal
+	 * commit function, which ensures that we never steal the display from
+	 * an active drm master.
+	 */
+#ifdef __linux__
+	force = var->activate & FB_ACTIVATE_KD_TEXT;
+#else
+	force = true;
+#endif
+
+	__drm_fb_helper_restore_fbdev_mode_unlocked(fb_helper, force);
 
 	return 0;
 }