xenvm: drivers: serial: Add consoleio Xen serial driver for Domain 0

This commit adds Xen consoleio serial driver. It is needed to receive
kernel messages from Zephyr in case it runs as Xen privileged domain
(Dom0). There is no console ring buffer for such domain, so regular
uart_hvc_xen driver can not be used (privileged domain input/output
are possible only through consoleio interface).

Signed-off-by: Dmytro Firsov <dmytro_firsov@epam.com>

CODEOWNERS

@@ -344,6 +344,7 @@
 /drivers/serial/serial_test.c             @str4t0m
 /drivers/serial/Kconfig.xen               @lorc @firscity
 /drivers/serial/uart_hvc_xen.c            @lorc @firscity
+/drivers/serial/uart_hvc_xen_consoleio.c  @lorc @firscity
 /drivers/serial/Kconfig.it8xxx2           @GTLin08
 /drivers/serial/uart_ite_it8xxx2.c        @GTLin08
 /drivers/disk/                            @jfischer-no

boards/arm64/xenvm/Kconfig.defconfig

@@ -6,6 +6,12 @@ if BOARD_XENVM
 config BUILD_OUTPUT_BIN
 	default y
 
+config XEN_INITIAL_DOMAIN
+	bool "Zephyr as Xen Domain 0"
+	default n
+	help
+	  Built binary will be used as Xen privileged domain.
+
 config BOARD
 	default "xenvm"
 

drivers/serial/CMakeLists.txt

@@ -45,6 +45,7 @@ zephyr_library_sources_ifdef(CONFIG_UART_XEC uart_mchp_xec.c)
 zephyr_library_sources_ifdef(CONFIG_UART_NEORV32 uart_neorv32.c)
 zephyr_library_sources_ifdef(CONFIG_USART_GD32 usart_gd32.c)
 zephyr_library_sources_ifdef(CONFIG_UART_XEN_HVC uart_hvc_xen.c)
+zephyr_library_sources_ifdef(CONFIG_UART_XEN_HVC_CONSOLEIO uart_hvc_xen_consoleio.c)
 
 zephyr_library_sources_ifdef(CONFIG_USERSPACE   uart_handlers.c)
 

drivers/serial/Kconfig.xen

@@ -5,17 +5,29 @@
 #
 
 config UART_XEN_HVC
-	bool "Xen hypervisor console UART Driver"
+	bool "Xen hypervisor DomU console UART driver"
 	select SERIAL_HAS_DRIVER
 	select SERIAL_SUPPORT_INTERRUPT
 	depends on BOARD_XENVM
+	depends on !XEN_INITIAL_DOMAIN
 	default y
 	help
-	  Enable Xen hypervisor console driver.
+	  Enable Xen ring buffer based hypervisor console driver. Used
+	  for Zephyr as unprivileged domain.
+
+config UART_XEN_HVC_CONSOLEIO
+	bool "Xen hypervisor Dom0 console UART driver"
+	select SERIAL_HAS_DRIVER
+	depends on BOARD_XENVM
+	depends on XEN_INITIAL_DOMAIN
+	default y
+	help
+	  Enable Xen hypervisor console driver. Used for Zephyr as
+	  privileged domain (Dom0).
 
 config XEN_HVC_INIT_PRIORITY
 	int "Xen hypervisor console init priority"
-	depends on UART_XEN_HVC
+	depends on UART_XEN_HVC || UART_XEN_HVC_CONSOLEIO
 	default 55
 	help
 	  Set init priority for Xen HVC, should be inited before UART
@@ -24,6 +36,7 @@ config XEN_HVC_INIT_PRIORITY
 config XEN_EARLY_CONSOLEIO
 	bool "Early printk/stdout through console_io Xen interface"
 	depends on BOARD_XENVM
+	depends on UART_XEN_HVC
 	default n
 	help
 	  Enable setting of console_io symbol hook for stdout and printk.

drivers/serial/uart_hvc_xen_consoleio.c

@@ -0,0 +1,55 @@
+/*
+ * Copyright (c) 2021 EPAM Systems
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * This driver implements input/output API for Xen domain through the
+ * Xen consoleio interface. This should be used only for Zephyr as initial
+ * domain (Dom0). For unprivileged domains regular ring buffer HVC driver
+ * should be used (uart_hvc_xen.c), this console will not be available.
+ */
+
+#include <arch/arm64/hypercall.h>
+#include <xen/public/xen.h>
+
+#include <device.h>
+#include <drivers/uart.h>
+#include <init.h>
+#include <kernel.h>
+
+static int xen_consoleio_poll_in(const struct device *dev,
+			unsigned char *c)
+{
+	int ret = 0;
+	char temp;
+
+	ret = HYPERVISOR_console_io(CONSOLEIO_read, sizeof(temp), &temp);
+	if (!ret) {
+		/* Char was not received */
+		return -1;
+	}
+
+	*c = temp;
+	return 0;
+}
+
+static void xen_consoleio_poll_out(const struct device *dev,
+			unsigned char c)
+{
+	(void) HYPERVISOR_console_io(CONSOLEIO_write, sizeof(c), &c);
+}
+
+static const struct uart_driver_api xen_consoleio_hvc_api = {
+	.poll_in = xen_consoleio_poll_in,
+	.poll_out = xen_consoleio_poll_out,
+};
+
+int xen_consoleio_init(const struct device *dev)
+{
+	/* Nothing to do, but still needed for device API */
+	return 0;
+}
+
+DEVICE_DT_DEFINE(DT_NODELABEL(xen_consoleio_hvc), xen_consoleio_init, NULL, NULL,
+		NULL, PRE_KERNEL_1, CONFIG_XEN_HVC_INIT_PRIORITY,
+		&xen_consoleio_hvc_api);