[riscv] Add support for the SBI debug console

Add the ability to issue Supervisor Binary Interface (SBI) calls via
the ECALL instruction, and use the SBI DBCN extension to implement a
debug console.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

1 files changed, 101 insertions, 0 deletions

diff --git a/src/arch/riscv/interface/sbi/sbi_console.c b/src/arch/riscv/interface/sbi/sbi_console.c
new file mode 100644
index 000000000..835255559
--- /dev/null
+++ b/src/arch/riscv/interface/sbi/sbi_console.c
@@ -0,0 +1,101 @@
+/*
+ * Copyright (C) 2024 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ *
+ * You can also choose to distribute this program under the terms of
+ * the Unmodified Binary Distribution Licence (as given in the file
+ * COPYING.UBDL), provided that you have satisfied its requirements.
+ */
+
+/** @file
+ *
+ * SBI debug console
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <ipxe/sbi.h>
+#include <ipxe/io.h>
+#include <ipxe/console.h>
+#include <config/console.h>
+
+/* Set default console usage if applicable */
+#if ! ( defined ( CONSOLE_SBI ) && CONSOLE_EXPLICIT ( CONSOLE_SBI ) )
+#undef CONSOLE_SBI
+#define CONSOLE_SBI ( CONSOLE_USAGE_ALL & ~CONSOLE_USAGE_LOG )
+#endif
+
+/** Buffered input character (if any) */
+static unsigned char sbi_console_input;
+
+/**
+ * Print a character to SBI console
+ *
+ * @v character		Character to be printed
+ */
+static void sbi_putchar ( int character ) {
+
+	/* Write byte to console */
+	sbi_ecall_1 ( SBI_DBCN, SBI_DBCN_WRITE_BYTE, character );
+}
+
+/**
+ * Get character from SBI console
+ *
+ * @ret character	Character read from console, if any
+ */
+static int sbi_getchar ( void ) {
+	int character;
+
+	/* Consume and return buffered character, if any */
+	character = sbi_console_input;
+	sbi_console_input = 0;
+	return character;
+}
+
+/**
+ * Check for character ready to read from SBI console
+ *
+ * @ret True		Character available to read
+ * @ret False		No character available to read
+ */
+static int sbi_iskey ( void ) {
+	struct sbi_return ret;
+
+	/* Do nothing if we already have a buffered character */
+	if ( sbi_console_input )
+		return sbi_console_input;
+
+	/* Read and buffer byte from console, if any */
+	ret = sbi_ecall_3 ( SBI_DBCN, SBI_DBCN_READ,
+			    sizeof ( sbi_console_input ),
+			    virt_to_phys ( &sbi_console_input ), 0 );
+	if ( ret.error )
+		return 0;
+
+	/* Return number of characters read and buffered */
+	return ret.value;
+}
+
+/** SBI console */
+struct console_driver sbi_console_driver __console_driver = {
+	.putchar = sbi_putchar,
+	.getchar = sbi_getchar,
+	.iskey = sbi_iskey,
+	.usage = CONSOLE_SBI,
+};