kernel: add RISC-V HTIF code

Change-Id: I83251bb4586b4f752c97741f62a96d2f6f842377
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4055
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>

src/system/kernel/arch/riscv64/Htif.cpp

@@ -0,0 +1,52 @@
+/*
+ * Copyright 2021, Haiku, Inc. All rights reserved.
+ * Distributed under the terms of the MIT License.
+ */
+
+
+#include <Htif.h>
+
+
+uint64
+HtifCmd(uint32 device, uint8 cmd, uint32 arg)
+{
+	if (gHtifRegs == 0)
+		return 0;
+
+	uint64 htifTohost = ((uint64)device << 56)
+		+ ((uint64)cmd << 48) + arg;
+	gHtifRegs->toHostLo = htifTohost % ((uint64)1 << 32);
+	gHtifRegs->toHostHi = htifTohost / ((uint64)1 << 32);
+	return (uint64)gHtifRegs->fromHostLo
+		+ ((uint64)gHtifRegs->fromHostHi << 32);
+}
+
+
+void
+HtifShutdown()
+{
+	HtifCmd(0, 0, 1);
+}
+
+
+void
+HtifOutChar(char ch)
+{
+	HtifCmd(1, 1, ch);
+}
+
+
+void
+HtifOutString(const char *str)
+{
+	for (; *str != '\0'; str++)
+		HtifOutChar(*str);
+}
+
+
+void
+HtifOutString(const char *str, size_t len)
+{
+	for (; len > 0; str++, len--)
+		HtifOutChar(*str);
+}

src/system/kernel/arch/riscv64/Jamfile

@@ -21,6 +21,7 @@ KernelMergeObject kernel_arch_riscv64.o :
         arch_vm.cpp
         arch_vm_translation_map.cpp
         RISCV64VMTranslationMap.cpp
+        Htif.cpp
         :
         $(TARGET_KERNEL_PIC_CCFLAGS) -Wno-unused
         :