[PATCH 09/11] drm/crtc: workaround userspace trying to derail crtc stealing

[Dave Airlie <airlied@gmail.com>]

From: Dave Airlie <airlied@redhat.com>

This is probably not the greatest idea in the world, but if userspace
does a modesetting sequences

initial state : crtc 0 -> eDP-1
modeset : crtc 1 -> DP-4 (dual crtc)
we have to steal crtc 2 for DP-3
modeset : crtc 2 -> eDP-1

we are kind off stuck, so when we see this, we back up the crtc
configuration, proceed with the userspace modeset, then do
the second modeset on the released crtc 0.

Signed-off-by: Dave Airlie <airlied@redhat.com>
---
 drivers/gpu/drm/drm_crtc.c | 107 ++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 102 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index 628f3af..e30518b 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -2509,6 +2509,91 @@ int drm_crtc_check_viewport(const struct drm_crtc *crtc,
 }
 EXPORT_SYMBOL(drm_crtc_check_viewport);
 
+static int drm_mode_get_crtc_set(struct drm_crtc *crtc, struct drm_mode_set *backup_set)
+{
+	struct drm_device *dev = crtc->dev;
+	struct drm_display_mode *mode;
+	struct drm_connector *connector;
+	int num_connectors = 0;
+	int i;
+
+	backup_set->crtc = crtc;
+	backup_set->x = crtc->x;
+	backup_set->y = crtc->y;
+	backup_set->fb = crtc->primary->fb;
+
+	mode = drm_mode_create(dev);
+	if (!mode) {
+		return -ENOMEM;
+	}
+
+	*mode = crtc->mode;
+	backup_set->mode = mode;
+
+	list_for_each_entry(connector, &dev->mode_config.connector_list, head) {
+		if (!connector->encoder)
+			continue;
+		if (!connector->encoder->crtc)
+			continue;
+
+		if (connector->encoder->crtc == crtc)
+			num_connectors++;
+	}
+
+	backup_set->connectors = kmalloc(num_connectors * sizeof(struct drm_connector *), GFP_KERNEL);
+	if (!backup_set->connectors) {
+		drm_mode_destroy(dev, mode);
+		return -ENOMEM;
+	}
+
+	i = 0;
+	list_for_each_entry(connector, &dev->mode_config.connector_list, head) {
+		if (!connector->encoder)
+			continue;
+		if (!connector->encoder->crtc)
+			continue;
+
+		if (connector->encoder->crtc == crtc)
+			backup_set->connectors[i++] = connector;
+	}
+
+	backup_set->num_connectors = i;
+	return 0;
+}
+
+static int drm_mode_reset_tiled_crtc(struct drm_mode_set *backup_set,
+				     struct drm_crtc *tile_master)
+{
+	struct drm_crtc *crtc2, *pick_crtc = NULL;
+	struct drm_device *dev = backup_set->crtc->dev;
+	int ret;
+	/* first up we need to find another crtc to use */
+	list_for_each_entry(crtc2, &dev->mode_config.crtc_list, head) {
+		if (crtc2 == backup_set->crtc)
+			continue;
+		if (crtc2->enabled && !crtc2->tile_master)
+			continue;
+		pick_crtc = crtc2;
+		break;
+	}
+
+	if (!pick_crtc) {
+		DRM_DEBUG_KMS("unable to find backup crtc\n");
+		goto out;
+
+	}
+
+	backup_set->crtc = pick_crtc;
+
+	pick_crtc->tile_master = tile_master;
+	list_add_tail(&pick_crtc->tile, &tile_master->tile_crtc_list);
+
+	ret = drm_mode_set_config_internal(backup_set);
+out:
+	kfree(backup_set->connectors);
+	return 0;
+}
+
 /* tiled variants */
 static int drm_mode_setcrtc_tiled(struct drm_mode_set *orig_set)
 {
@@ -2631,6 +2716,9 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
 	struct drm_framebuffer *fb = NULL;
 	struct drm_display_mode *mode = NULL;
 	struct drm_mode_set set;
+	struct drm_mode_set tile_backup_set;
+	struct drm_crtc *backup_tile_master = NULL;
+	bool rework_backup = false;
 	uint32_t __user *set_connectors_ptr;
 	int ret;
 	int i;
@@ -2653,12 +2741,17 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
 	DRM_DEBUG_KMS("[CRTC:%d]\n", crtc->base.id);
 
 	if (crtc->tile_master) {
-		if (crtc_req->mode_valid)
-			ret = -EBUSY;
-		else
+		if (!crtc_req->mode_valid) {
 			ret = 0;
-		DRM_DEBUG_KMS("[CRTC:%d] refused due to tile %d\n", crtc->base.id, ret);
-		goto out;
+			goto out;
+		}
+
+		drm_mode_get_crtc_set(crtc, &tile_backup_set);
+		DRM_DEBUG_KMS("[CRTC:%d] backing up tiling\n", crtc->base.id);
+		rework_backup = true;
+		backup_tile_master = crtc->tile_master;
+		crtc->tile_master = false;
+		list_del(&crtc->tile);
 	}
 
 	if (crtc_req->mode_valid) {
@@ -2791,6 +2884,10 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
 		}
 		ret = drm_mode_set_config_internal(&set);
 	}
+
+	if (rework_backup) {
+		drm_mode_reset_tiled_crtc(&tile_backup_set, backup_tile_master);
+	}
 out:
 	if (fb)
 		drm_framebuffer_unreference(fb);
-- 
1.9.3