rockchip: video: Check for device in use

Check whether a display device is in use before using it. Add a comment as
to why two displays cannot currently be used at the same time.

This allows us to remove the device-tree change that disables vopb on
jerry.

Signed-off-by: Simon Glass <sjg@chromium.org>

arch/arm/dts/rk3288-jerry.dts

@@ -108,11 +108,6 @@
 	pinctrl-0 = <&vcc50_hdmi_en>;
 };
 
-&vopb {
-	/* Disable this so that we use vopl */
-	status = "disabled";
-};
-
 &edp {
 	pinctrl-names = "default";
 	pinctrl-0 = <&edp_hpd>;

arch/arm/dts/rk3288-veyron-chromebook.dtsi

@@ -13,6 +13,8 @@
 / {
 	aliases {
 		i2c20 = &i2c_tunnel;
+		video0 = &vopl;
+		video1 = &vopb;
 	};
 
 	gpio_keys: gpio-keys {

drivers/video/rockchip/rk_vop.c

@@ -221,6 +221,11 @@ int rk_display_init(struct udevice *dev, ulong fbbase,
 
 	disp_uc_plat = dev_get_uclass_platdata(disp);
 	debug("Found device '%s', disp_uc_priv=%p\n", disp->name, disp_uc_plat);
+	if (display_in_use(disp)) {
+		debug("   - device in use\n");
+		return -EBUSY;
+	}
+
 	disp_uc_plat->source_id = remote_vop_id;
 	disp_uc_plat->src_dev = dev;
 
@@ -311,6 +316,10 @@ static int rk_vop_probe(struct udevice *dev)
 	/*
 	 * Try all the ports until we find one that works. In practice this
 	 * tries EDP first if available, then HDMI.
+	 *
+	 * Note that rockchip_vop_set_clk() always uses NPLL as the source
+	 * clock so it is currently not possible to use more than one display
+	 * device simultaneously.
 	 */
 	port = fdt_subnode_offset(blob, dev->of_offset, "port");
 	if (port < 0)