[PATCH v3 4/6] lib: sbi: Implement SBI debug console extension

[Anup Patel <apatel@ventanamicro.com>]

We implement SBI debug console extension as one of the replacement
SBI extensions. This extension is only available when OpenSBI platform
provides a console device to generic library.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
---
 lib/sbi/Kconfig          |  4 +++
 lib/sbi/objects.mk       |  3 ++
 lib/sbi/sbi_ecall_dbcn.c | 62 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 69 insertions(+)
 create mode 100644 lib/sbi/sbi_ecall_dbcn.c

diff --git a/lib/sbi/Kconfig b/lib/sbi/Kconfig
index df74bba..ef6728b 100644
--- a/lib/sbi/Kconfig
+++ b/lib/sbi/Kconfig
@@ -26,6 +26,10 @@ config SBI_ECALL_PMU
 	bool "Performance Monitoring Unit extension"
 	default y
 
+config SBI_ECALL_DBCN
+	bool "Debug Console extension"
+	default y
+
 config SBI_ECALL_LEGACY
 	bool "SBI v0.1 legacy extensions"
 	default y
diff --git a/lib/sbi/objects.mk b/lib/sbi/objects.mk
index c774ebb..319f38d 100644
--- a/lib/sbi/objects.mk
+++ b/lib/sbi/objects.mk
@@ -37,6 +37,9 @@ libsbi-objs-$(CONFIG_SBI_ECALL_SRST) += sbi_ecall_srst.o
 carray-sbi_ecall_exts-$(CONFIG_SBI_ECALL_PMU) += ecall_pmu
 libsbi-objs-$(CONFIG_SBI_ECALL_PMU) += sbi_ecall_pmu.o
 
+carray-sbi_ecall_exts-$(CONFIG_SBI_ECALL_DBCN) += ecall_dbcn
+libsbi-objs-$(CONFIG_SBI_ECALL_DBCN) += sbi_ecall_dbcn.o
+
 carray-sbi_ecall_exts-$(CONFIG_SBI_ECALL_LEGACY) += ecall_legacy
 libsbi-objs-$(CONFIG_SBI_ECALL_LEGACY) += sbi_ecall_legacy.o
 
diff --git a/lib/sbi/sbi_ecall_dbcn.c b/lib/sbi/sbi_ecall_dbcn.c
new file mode 100644
index 0000000..19ac021
--- /dev/null
+++ b/lib/sbi/sbi_ecall_dbcn.c
@@ -0,0 +1,62 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2022 Ventana Micro Systems Inc.
+ *
+ * Authors:
+ *   Anup Patel <apatel@ventanamicro.com>
+ */
+
+#include <sbi/sbi_console.h>
+#include <sbi/sbi_domain.h>
+#include <sbi/sbi_error.h>
+#include <sbi/sbi_ecall.h>
+#include <sbi/sbi_ecall_interface.h>
+#include <sbi/sbi_trap.h>
+#include <sbi/riscv_asm.h>
+
+static int sbi_ecall_dbcn_handler(unsigned long extid, unsigned long funcid,
+				  const struct sbi_trap_regs *regs,
+				  unsigned long *out_val,
+				  struct sbi_trap_info *out_trap)
+{
+	ulong smode = (csr_read(CSR_MSTATUS) & MSTATUS_MPP) >>
+			MSTATUS_MPP_SHIFT;
+
+	if (funcid == SBI_EXT_DBCN_CONSOLE_PUTS) {
+		/*
+		 * On RV32, the M-mode can only access the first 4GB of
+		 * the physical address space because M-mode does not have
+		 * MMU to access full 34-bit physical address space.
+		 *
+		 * Based on above, we simply fail if the upper 32bits of
+		 * the physical address (i.e. a2 register) is non-zero on
+		 * RV32.
+		 */
+#if __riscv_xlen == 32
+		if (regs->a2)
+			return SBI_ERR_FAILED;
+#endif
+		if (!sbi_domain_check_addr_range(sbi_domain_thishart_ptr(),
+					regs->a1, regs->a0, smode,
+					SBI_DOMAIN_READ|SBI_DOMAIN_WRITE))
+			return SBI_EINVALID_ADDR;
+		sbi_nputs((const char *)regs->a1, regs->a0);
+		return 0;
+	}
+
+	return SBI_ENOTSUPP;
+}
+
+static int sbi_ecall_dbcn_probe(unsigned long extid, unsigned long *out_val)
+{
+	*out_val = (sbi_console_get_device()) ? 1 : 0;
+	return 0;
+}
+
+struct sbi_ecall_extension ecall_dbcn = {
+	.extid_start = SBI_EXT_DBCN,
+	.extid_end = SBI_EXT_DBCN,
+	.handle = sbi_ecall_dbcn_handler,
+	.probe = sbi_ecall_dbcn_probe,
+};
-- 
2.34.1