[PATCH] drm/client: Use common display mode for cloned outputs

[Thomas Zimmermann <tzimmermann@xxxxxxx>]

For cloned outputs, don't pick a default resolution of 1024x768 as
most hardware can do better. Instead look through the modes of all
connectors to find a common mode for all of them.

Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
---
 drivers/gpu/drm/drm_client_modeset.c | 54 +++++++++++++++++-----------
 1 file changed, 34 insertions(+), 20 deletions(-)

diff --git a/drivers/gpu/drm/drm_client_modeset.c b/drivers/gpu/drm/drm_client_modeset.c
index 31af5cf37a09..67b422dc8e7f 100644
--- a/drivers/gpu/drm/drm_client_modeset.c
+++ b/drivers/gpu/drm/drm_client_modeset.c
@@ -266,7 +266,7 @@ static bool drm_client_target_cloned(struct drm_device *dev,
 {
 	int count, i, j;
 	bool can_clone = false;
-	struct drm_display_mode *dmt_mode, *mode;
+	struct drm_display_mode *mode, *common_mode = NULL;
 
 	/* only contemplate cloning in the single crtc case */
 	if (dev->mode_config.num_crtc > 1)
@@ -309,35 +309,49 @@ static bool drm_client_target_cloned(struct drm_device *dev,
 		return true;
 	}
 
-	/* try and find a 1024x768 mode on each connector */
-	can_clone = true;
-	dmt_mode = drm_mode_find_dmt(dev, 1024, 768, 60, false);
-
-	if (!dmt_mode)
-		goto fail;
+	/* try and find a mode common among connectors */
 
+	can_clone = false;
 	for (i = 0; i < connector_count; i++) {
 		if (!enabled[i])
 			continue;
 
-		list_for_each_entry(mode, &connectors[i]->modes, head) {
-			if (drm_mode_match(mode, dmt_mode,
-					   DRM_MODE_MATCH_TIMINGS |
-					   DRM_MODE_MATCH_CLOCK |
-					   DRM_MODE_MATCH_FLAGS |
-					   DRM_MODE_MATCH_3D_FLAGS))
-				modes[i] = mode;
+		list_for_each_entry(common_mode, &connectors[i]->modes, head) {
+			can_clone = true;
+
+			for (j = 1; j < connector_count; j++) {
+				if (!enabled[i])
+					continue;
+
+				can_clone = false;
+				list_for_each_entry(mode, &connectors[j]->modes, head) {
+					can_clone = drm_mode_match(common_mode, mode,
+								   DRM_MODE_MATCH_TIMINGS |
+							    DRM_MODE_MATCH_CLOCK |
+							    DRM_MODE_MATCH_FLAGS |
+							    DRM_MODE_MATCH_3D_FLAGS);
+					if (can_clone)
+						break; // found common mode on connector
+				}
+				if (!can_clone)
+					break; // try next common mode
+			}
+			if (can_clone)
+				break; // found common mode among all connectors
 		}
-		if (!modes[i])
-			can_clone = false;
+		break;
 	}
-	kfree(dmt_mode);
-
 	if (can_clone) {
-		drm_dbg_kms(dev, "can clone using 1024x768\n");
+		for (i = 0; i < connector_count; i++) {
+			if (!enabled[i])
+				continue;
+			modes[i] = common_mode;
+
+		}
+		drm_dbg_kms(dev, "can clone using" DRM_MODE_FMT "\n", DRM_MODE_ARG(common_mode));
 		return true;
 	}
-fail:
+
 	drm_info(dev, "kms: can't enable cloning when we probably wanted to.\n");
 	return false;
 }
-- 
2.45.2