From 2a52409cba31a1d5709451eceedfa7c8868bcfb8 Mon Sep 17 00:00:00 2001
From: Joel Severin <joel.severin@icemanor.se>
Date: Sun, 30 Jun 2024 00:47:26 +0200
Subject: [PATCH] Add Wasm console support

Adds a simple HVC + earlycon tty driver that calls out to the Wasm host
using simple exported functions on the vmlinux Module for reads/writes.
---
 arch/wasm/Kconfig            |  2 +-
 arch/wasm/Makefile           |  1 +
 arch/wasm/drivers/Kconfig    | 22 ++++++++++++++++++++++
 arch/wasm/drivers/Makefile   |  3 +++
 arch/wasm/drivers/hvc_wasm.c | 35 +++++++++++++++++++++++++++++++++++
 5 files changed, 62 insertions(+), 1 deletion(-)
 create mode 100644 arch/wasm/drivers/Kconfig
 create mode 100644 arch/wasm/drivers/Makefile
 create mode 100644 arch/wasm/drivers/hvc_wasm.c

diff --git a/arch/wasm/Kconfig b/arch/wasm/Kconfig
index 744e8c676..2e01d91b3 100644
--- a/arch/wasm/Kconfig
+++ b/arch/wasm/Kconfig
@@ -77,4 +77,4 @@ config ARCH_HAVE_PANIC_NOTIFY
 
 endmenu
 
-source "drivers/Kconfig"
+source "arch/wasm/drivers/Kconfig"
diff --git a/arch/wasm/Makefile b/arch/wasm/Makefile
index b86103e0b..841f3b006 100644
--- a/arch/wasm/Makefile
+++ b/arch/wasm/Makefile
@@ -12,6 +12,7 @@ KCFLAGS += -Xclang -target-feature -Xclang +bulk-memory
 core-y += arch/wasm/kernel/
 core-y += arch/wasm/mm/
 libs-y += arch/wasm/lib/
+drivers-y += arch/wasm/drivers/
 
 PHONY += bzImage
 
diff --git a/arch/wasm/drivers/Kconfig b/arch/wasm/drivers/Kconfig
new file mode 100644
index 000000000..be8b75496
--- /dev/null
+++ b/arch/wasm/drivers/Kconfig
@@ -0,0 +1,22 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+menu "Wasm Character Devices"
+
+config HVC_WASM
+	bool "Wasm console support"
+	select HVC_DRIVER
+	help
+	  This config option enables support for a console managed by the Wasm
+	  host, for example to read printk output during boot as well as
+	  receiving user input. It works both as an earlycon and a tty. As an
+	  earlycon, very early debug logging is output. As a tty (enabled later
+	  on in the boot process), it also supports user input from the host.
+
+	  In addition to enabling this config option at build time, you also
+	  need to specify console=hvc as a parameter on the kernel command line
+	  to activate the feature at runtime. Just specifying console=hvc is
+	  enough to enable the earlycon aspects of this console driver as well.
+
+	  If you don't know what to do here, say Y.
+
+endmenu
diff --git a/arch/wasm/drivers/Makefile b/arch/wasm/drivers/Makefile
new file mode 100644
index 000000000..0ebdc20a8
--- /dev/null
+++ b/arch/wasm/drivers/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+obj-$(CONFIG_HVC_WASM) += hvc_wasm.o
diff --git a/arch/wasm/drivers/hvc_wasm.c b/arch/wasm/drivers/hvc_wasm.c
new file mode 100644
index 000000000..78f34c060
--- /dev/null
+++ b/arch/wasm/drivers/hvc_wasm.c
@@ -0,0 +1,35 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include "../../../drivers/tty/hvc/hvc_console.h"
+
+extern int wasm_driver_hvc_put(const char *buf, int count);
+extern int wasm_driver_hvc_get(char *buf, int count);
+
+static int hvc_wasm_put_chars(uint32_t vtermno, const char *buf, int count)
+{
+	return wasm_driver_hvc_put(buf, count);
+}
+
+static int hvc_wasm_get_chars(uint32_t vtermno, char *buf, int count)
+{
+	return wasm_driver_hvc_get(buf, count);
+}
+
+static const struct hv_ops hvc_wasm_ops = {
+	.get_chars = hvc_wasm_get_chars,
+	.put_chars = hvc_wasm_put_chars,
+};
+
+static int __init hvc_wasm_init(void)
+{
+	return PTR_ERR_OR_ZERO(hvc_alloc(0, 0, &hvc_wasm_ops, PAGE_SIZE));
+}
+device_initcall(hvc_wasm_init);
+
+static int __init hvc_wasm_console_init(void)
+{
+	hvc_instantiate(0, 0, &hvc_wasm_ops);
+
+	return 0;
+}
+console_initcall(hvc_wasm_console_init);
-- 
2.25.1