xen: add files needed for minimal riscv build

Add arch-specific makefiles and configs needed to build for
riscv. Also add a minimal head.S that is a simple infinite loop.
head.o can be built with

$ make XEN_TARGET_ARCH=riscv64 SUBSYSTEMS=xen -C xen tiny64_defconfig
$ make XEN_TARGET_ARCH=riscv64 SUBSYSTEMS=xen -C xen TARGET=riscv64/head.o

No other TARGET is supported at the moment.

Signed-off-by: Connor Davis <connojdavis@gmail.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Acked-by: Bobby Eshleman <bobbyeshleman@gmail.com>

MAINTAINERS

@@ -456,6 +456,15 @@ F:	tools/libs/light/libxl_nonetbuffer.c
 F:	tools/hotplug/Linux/remus-netbuf-setup
 F:	tools/hotplug/Linux/block-drbd-probe
 
+RISCV
+M:	Bob Eshleman <bobbyeshleman@gmail.com>
+M:	Alistair Francis <alistair.francis@wdc.com>
+R:	Connor Davis <connojdavis@gmail.com>
+S:	Supported
+F:	config/riscv64.mk
+F:	xen/arch/riscv/
+F:	xen/include/asm-riscv/
+
 RTDS SCHEDULER
 M:	Dario Faggioli <dfaggioli@suse.com>
 M:	Meng Xu <mengxu@cis.upenn.edu>

config/riscv64.mk

@@ -0,0 +1,5 @@
+CONFIG_RISCV := y
+CONFIG_RISCV_64 := y
+CONFIG_RISCV_$(XEN_OS) := y
+
+CONFIG_XEN_INSTALL_SUFFIX :=

xen/Makefile

@@ -26,7 +26,9 @@ MAKEFLAGS += -rR
 EFI_MOUNTPOINT ?= $(BOOT_DIR)/efi
 
 ARCH=$(XEN_TARGET_ARCH)
-SRCARCH=$(shell echo $(ARCH) | sed -e 's/x86.*/x86/' -e s'/arm\(32\|64\)/arm/g')
+SRCARCH=$(shell echo $(ARCH) | \
+          sed -e 's/x86.*/x86/' -e s'/arm\(32\|64\)/arm/g' \
+              -e s'/riscv.*/riscv/g')
 
 # Don't break if the build process wasn't called from the top level
 # we need XEN_TARGET_ARCH to generate the proper config
@@ -35,7 +37,8 @@ include $(XEN_ROOT)/Config.mk
 # Set ARCH/SUBARCH appropriately.
 export TARGET_SUBARCH  := $(XEN_TARGET_ARCH)
 export TARGET_ARCH     := $(shell echo $(XEN_TARGET_ARCH) | \
-                            sed -e 's/x86.*/x86/' -e s'/arm\(32\|64\)/arm/g')
+                            sed -e 's/x86.*/x86/' -e s'/arm\(32\|64\)/arm/g' \
+                                -e s'/riscv.*/riscv/g')
 
 # Allow someone to change their config file
 export KCONFIG_CONFIG ?= .config
@@ -335,6 +338,7 @@ _clean: delete-unfresh-files
 	$(MAKE) $(clean) xsm
 	$(MAKE) $(clean) crypto
 	$(MAKE) $(clean) arch/arm
+	$(MAKE) $(clean) arch/riscv
 	$(MAKE) $(clean) arch/x86
 	$(MAKE) $(clean) test
 	$(MAKE) -f $(BASEDIR)/tools/kconfig/Makefile.kconfig ARCH=$(ARCH) SRCARCH=$(SRCARCH) clean

xen/arch/riscv/Kconfig

@@ -0,0 +1,48 @@
+config RISCV
+	def_bool y
+
+config RISCV_64
+	def_bool y
+	select 64BIT
+
+config ARCH_DEFCONFIG
+	string
+	default "arch/riscv/configs/tiny64_defconfig"
+
+menu "Architecture Features"
+
+source "arch/Kconfig"
+
+endmenu
+
+menu "ISA Selection"
+
+choice
+	prompt "Base ISA"
+	default RISCV_ISA_RV64IMA if RISCV_64
+	help
+	  This selects the base ISA extensions that Xen will target.
+
+config RISCV_ISA_RV64IMA
+	bool "RV64IMA"
+	help
+	  Use the RV64I base ISA, plus the "M" and "A" extensions
+	  for integer multiply/divide and atomic instructions, respectively.
+
+endchoice
+
+config RISCV_ISA_C
+	bool "Compressed extension"
+	default y
+	help
+	  Add "C" to the ISA subsets that the toolchain is allowed to
+	  emit when building Xen, which results in compressed instructions
+	  in the Xen binary.
+
+	  If unsure, say Y.
+
+endmenu
+
+source "common/Kconfig"
+
+source "drivers/Kconfig"

xen/arch/riscv/Makefile

@@ -0,0 +1,2 @@
+.PHONY: include
+include:

xen/arch/riscv/arch.mk

@@ -0,0 +1,14 @@
+########################################
+# RISCV-specific definitions
+
+CFLAGS-$(CONFIG_RISCV_64) += -mabi=lp64
+
+riscv-march-$(CONFIG_RISCV_ISA_RV64IMA) := rv64ima
+riscv-march-$(CONFIG_RISCV_ISA_C)       := $(riscv-march-y)c
+
+# Note that -mcmodel=medany is used so that Xen can be mapped
+# into the upper half _or_ the lower half of the address space.
+# -mcmodel=medlow would force Xen into the lower half.
+
+CFLAGS += -march=$(riscv-march-y) -mstrict-align -mcmodel=medany
+CFLAGS += -I$(BASEDIR)/include

xen/arch/riscv/configs/tiny64_defconfig

@@ -0,0 +1,13 @@
+# CONFIG_SCHED_CREDIT is not set
+# CONFIG_SCHED_RTDS is not set
+# CONFIG_SCHED_NULL is not set
+# CONFIG_SCHED_ARINC653 is not set
+# CONFIG_TRACEBUFFER is not set
+# CONFIG_HYPFS is not set
+# CONFIG_GRANT_TABLE is not set
+# CONFIG_SPECULATIVE_HARDEN_ARRAY is not set
+
+CONFIG_RISCV_64=y
+CONFIG_DEBUG=y
+CONFIG_DEBUG_INFO=y
+CONFIG_EXPERT=y

xen/arch/riscv/riscv64/head.S

@@ -0,0 +1,6 @@
+#include <asm/config.h>
+
+        .text
+
+ENTRY(start)
+        j  start

xen/include/asm-riscv/config.h

@@ -0,0 +1,47 @@
+#ifndef __RISCV_CONFIG_H__
+#define __RISCV_CONFIG_H__
+
+#if defined(CONFIG_RISCV_64)
+# define LONG_BYTEORDER 3
+# define ELFSIZE 64
+# define MAX_VIRT_CPUS 128u
+#else
+# error "Unsupported RISCV variant"
+#endif
+
+#define BYTES_PER_LONG (1 << LONG_BYTEORDER)
+#define BITS_PER_LONG  (BYTES_PER_LONG << 3)
+#define POINTER_ALIGN  BYTES_PER_LONG
+
+#define BITS_PER_LLONG 64
+
+/* xen_ulong_t is always 64 bits */
+#define BITS_PER_XEN_ULONG 64
+
+#define CONFIG_RISCV_L1_CACHE_SHIFT 6
+#define CONFIG_PAGEALLOC_MAX_ORDER  18
+#define CONFIG_DOMU_MAX_ORDER       9
+#define CONFIG_HWDOM_MAX_ORDER      10
+
+#define OPT_CONSOLE_STR "dtuart"
+#define INVALID_VCPU_ID MAX_VIRT_CPUS
+
+/* Linkage for RISCV */
+#ifdef __ASSEMBLY__
+#define ALIGN .align 2
+
+#define ENTRY(name)                                \
+  .globl name;                                     \
+  ALIGN;                                           \
+  name:
+#endif
+
+#endif /* __RISCV_CONFIG_H__ */
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * indent-tabs-mode: nil
+ * End:
+ */