samples: subsys: console: echo: Add VIRTIO Console overlay

Add overlay files for testing the VIRTIO Console device with
this sample along with a section in the README.

Signed-off-by: Jakub Klimczak <[email protected]>

Author: Jakub Klimczak

samples/subsys/console/echo/README.rst

@@ -33,6 +33,27 @@ board. Alternatively you can run this using QEMU, as described in
 Following the initial prompt given by the firmware, start pressing keys on a
 keyboard, and they will be echoed back to the terminal program you are using.
 
+Running on QEMU
+===============
+
+On QEMU you can use the VIRTIO console device. It is already configured in
+Zephyr. To use it, run:
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/subsys/console/echo
+   :board: qemu_x86_64
+   :gen-args: -DDTC_OVERLAY_FILE=virtconsole.overlay -DEXTRA_CONF_FILE=overlay-virtconsole.conf
+   :goals: run
+   :compact:
+
+It is possible to use multiple inputs/outputs at once by configuring them
+in the ``overlay-virtconsole.conf`` file.
+
+* Add ``CONFIG_UART_VIRTIO_CONSOLE_F_MULTIPORT=y`` to enable the
+  multiport feature.
+* Configure more ports using the ``CONFIG_QEMU_EXTRA_FLAGS`` option.
+  Refer to the QEMU manual for details.
+
 Sample Output
 =============
 

samples/subsys/console/echo/overlay-virtconsole.conf

@@ -0,0 +1,12 @@
+# Copyright (c) 2025 Antmicro <www.antmicro.com>
+# SPDX-License-Identifier: Apache-2.0
+
+CONFIG_VIRTIO=y
+CONFIG_PCIE=y
+CONFIG_UART_VIRTIO_CONSOLE=y
+CONFIG_HEAP_MEM_POOL_SIZE=32768
+
+# The VIRTIO console cannot be used as early console
+CONFIG_BOOT_BANNER=n
+CONFIG_EARLY_CONSOLE=n
+CONFIG_X86_VERY_EARLY_CONSOLE=n

samples/subsys/console/echo/virtconsole.overlay

@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) 2025 Antmicro <www.antmicro.com>
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/ {
+	chosen {
+		zephyr,console = &virtio_console;
+	};
+};
+
+&pcie0 {
+	virtio_pci: virtio_pci {
+		compatible = "virtio,pci";
+
+		vendor-id = <0x1af4>;
+		device-id = <0x1003>;
+
+		interrupts = <0xb 0x0 0x0>;
+		interrupt-parent = <&intc>;
+
+		virtio_console: virtio_console {
+			compatible = "virtio,console";
+			status = "okay";
+		};
+	};
+};