1 files changed, 51 insertions, 0 deletions
diff --git a/drivers/tty/serial/earlycon-arm-semihost.c b/drivers/tty/serial/earlycon-arm-semihost.c
new file mode 100644
index 000000000..fa096c10b
--- /dev/null
+++ b/drivers/tty/serial/earlycon-arm-semihost.c
@@ -0,0 +1,51 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2012 ARM Ltd.
+ * Author: Marc Zyngier <marc.zyngier@arm.com>
+ *
+ * Adapted for ARM and earlycon:
+ * Copyright (C) 2014 Linaro Ltd.
+ * Author: Rob Herring <robh@kernel.org>
+ */
+#include <linux/kernel.h>
+#include <linux/console.h>
+#include <linux/init.h>
+#include <linux/serial_core.h>
+
+#ifdef CONFIG_THUMB2_KERNEL
+#define SEMIHOST_SWI	"0xab"
+#else
+#define SEMIHOST_SWI	"0x123456"
+#endif
+
+/*
+ * Semihosting-based debug console
+ */
+static void smh_putc(struct uart_port *port, int c)
+{
+#ifdef CONFIG_ARM64
+	asm volatile("mov  x1, %0\n"
+		     "mov  x0, #3\n"
+		     "hlt  0xf000\n"
+		     : : "r" (&c) : "x0", "x1", "memory");
+#else
+	asm volatile("mov  r1, %0\n"
+		     "mov  r0, #3\n"
+		     "svc  " SEMIHOST_SWI "\n"
+		     : : "r" (&c) : "r0", "r1", "memory");
+#endif
+}
+
+static void smh_write(struct console *con, const char *s, unsigned n)
+{
+	struct earlycon_device *dev = con->data;
+	uart_console_write(&dev->port, s, n, smh_putc);
+}
+
+static int
+__init early_smh_setup(struct earlycon_device *device, const char *opt)
+{
+	device->con->write = smh_write;
+	return 0;
+}
+EARLYCON_DECLARE(smh, early_smh_setup);