drm/fbdev: Fallback to non tiled mode if all tiles not present

In case of tiled displays, if we hotplug just one connector,
fbcon currently just selects the preferred mode and if it is
tiled mode then that becomes a problem if rest of the tiles are
not present.
So in the fbdev driver on hotplug when we probe the client modeset,
if we dont find all the connectors for all tiles, then on a connector
with one tile, just fallback to the first available non tiled mode
to display over a single connector.
On the hotplug of the consecutive tiled connectors, if the tiled mode
no longer exists because of fbcon size limitation, then return
no modes for consecutive tiles but retain the non tiled mode
on the 0th tile.
Use the same logic in case of connected boot case as well.
This has been tested with Dell UP328K tiled monitor.

v3:
* Check Num tiled conns that are connected (Manasi)
v2:
* Set the modes on consecutive hotplugged tiles to no mode
if tiled mode is pruned (Dave)
v1:
* Just handle the 1st connector hotplug case
* v1 Reviewed-by: Dave Airlie <airlied@redhat.com>

Bugzilla: https://gitlab.freedesktop.org/drm/intel/issues/5
Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Suggested-by: Dave Airlie <airlied@redhat.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Dave Airlie <airlied@redhat.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Dave Airlie <airlied@redhat.com> (v2)
Link: https://patchwork.freedesktop.org/patch/msgid/20191211212433.18185-2-manasi.d.navare@intel.com

drivers/gpu/drm/drm_client_modeset.c

@@ -114,6 +114,33 @@ drm_client_find_modeset(struct drm_client_dev *client, struct drm_crtc *crtc)
 	return NULL;
 }
 
+static struct drm_display_mode *
+drm_connector_get_tiled_mode(struct drm_connector *connector)
+{
+	struct drm_display_mode *mode;
+
+	list_for_each_entry(mode, &connector->modes, head) {
+		if (mode->hdisplay == connector->tile_h_size &&
+		    mode->vdisplay == connector->tile_v_size)
+			return mode;
+	}
+	return NULL;
+}
+
+static struct drm_display_mode *
+drm_connector_fallback_non_tiled_mode(struct drm_connector *connector)
+{
+	struct drm_display_mode *mode;
+
+	list_for_each_entry(mode, &connector->modes, head) {
+		if (mode->hdisplay == connector->tile_h_size &&
+		    mode->vdisplay == connector->tile_v_size)
+			continue;
+		return mode;
+	}
+	return NULL;
+}
+
 static struct drm_display_mode *
 drm_connector_has_preferred_mode(struct drm_connector *connector, int width, int height)
 {
@@ -348,8 +375,15 @@ static bool drm_client_target_preferred(struct drm_connector **connectors,
 	struct drm_connector *connector;
 	u64 conn_configured = 0;
 	int tile_pass = 0;
+	int num_tiled_conns = 0;
 	int i;
 
+	for (i = 0; i < connector_count; i++) {
+		if (connectors[i]->has_tile &&
+		    connectors[i]->status == connector_status_connected)
+			num_tiled_conns++;
+	}
+
 retry:
 	for (i = 0; i < connector_count; i++) {
 		connector = connectors[i];
@@ -399,6 +433,28 @@ static bool drm_client_target_preferred(struct drm_connector **connectors,
 			list_for_each_entry(modes[i], &connector->modes, head)
 				break;
 		}
+		/*
+		 * In case of tiled mode if all tiles not present fallback to
+		 * first available non tiled mode.
+		 * After all tiles are present, try to find the tiled mode
+		 * for all and if tiled mode not present due to fbcon size
+		 * limitations, use first non tiled mode only for
+		 * tile 0,0 and set to no mode for all other tiles.
+		 */
+		if (connector->has_tile) {
+			if (num_tiled_conns <
+			    connector->num_h_tile * connector->num_v_tile ||
+			    (connector->tile_h_loc == 0 &&
+			     connector->tile_v_loc == 0 &&
+			     !drm_connector_get_tiled_mode(connector))) {
+				DRM_DEBUG_KMS("Falling back to non tiled mode on Connector %d\n",
+					      connector->base.id);
+				modes[i] = drm_connector_fallback_non_tiled_mode(connector);
+			} else {
+				modes[i] = drm_connector_get_tiled_mode(connector);
+			}
+		}
+
 		DRM_DEBUG_KMS("found mode %s\n", modes[i] ? modes[i]->name :
 			  "none");
 		conn_configured |= BIT_ULL(i);
@@ -515,6 +571,7 @@ static bool drm_client_firmware_config(struct drm_client_dev *client,
 	bool fallback = true, ret = true;
 	int num_connectors_enabled = 0;
 	int num_connectors_detected = 0;
+	int num_tiled_conns = 0;
 	struct drm_modeset_acquire_ctx ctx;
 
 	if (!drm_drv_uses_atomic_modeset(dev))
@@ -532,6 +589,11 @@ static bool drm_client_firmware_config(struct drm_client_dev *client,
 	memcpy(save_enabled, enabled, count);
 	mask = GENMASK(count - 1, 0);
 	conn_configured = 0;
+	for (i = 0; i < count; i++) {
+		if (connectors[i]->has_tile &&
+		    connectors[i]->status == connector_status_connected)
+			num_tiled_conns++;
+	}
 retry:
 	conn_seq = conn_configured;
 	for (i = 0; i < count; i++) {
@@ -631,6 +693,16 @@ static bool drm_client_firmware_config(struct drm_client_dev *client,
 				      connector->name);
 			modes[i] = &connector->state->crtc->mode;
 		}
+		/*
+		 * In case of tiled modes, if all tiles are not present
+		 * then fallback to a non tiled mode.
+		 */
+		if (connector->has_tile &&
+		    num_tiled_conns < connector->num_h_tile * connector->num_v_tile) {
+			DRM_DEBUG_KMS("Falling back to non tiled mode on Connector %d\n",
+				      connector->base.id);
+			modes[i] = drm_connector_fallback_non_tiled_mode(connector);
+		}
 		crtcs[i] = new_crtc;
 
 		DRM_DEBUG_KMS("connector %s on [CRTC:%d:%s]: %dx%d%s\n",