RISC-V: Implement option to run NuttX in supervisor mode (S-mode)

- Add config "ARCH_USE_S_MODE" which controls whether the kernel
  runs in M-mode or S-mode
- Add more MSTATUS and most of the SSTATUS register definitions
- Add more MIP flags for interrupt delegation
- Add handling of interrupts from S-mode
- Add handling of FPU from S-mode
- Add new context handling functions that are not dependent on the trap
  handlers / ecall

NOTE: S-mode requires a companion SW (SBI) which is not yet implemented,
      thus S-mode is not usable as is, yet.

arch/risc-v/Kconfig

@@ -101,6 +101,7 @@ config ARCH_CHIP_MPFS
 	select ARCH_HAVE_RESET
 	select ARCH_HAVE_SPI_CS_CONTROL
 	select ARCH_HAVE_PWM_MULTICHAN
+	select ARCH_HAVE_S_MODE
 	select PMP_HAS_LIMITED_FEATURES
 	---help---
 		MicroChip Polarfire processor (RISC-V 64bit core with GCVX extensions).
@@ -188,6 +189,27 @@ config ARCH_MMU_TYPE_SV39
 	bool
 	default n
 
+config ARCH_HAVE_S_MODE
+	bool
+	default n
+
+# Option to run NuttX in supervisor mode. This is obviously not usable in
+# flat mode, is questionable in protected mode, but is mandatory in kernel
+# mode.
+#
+# Kernel mode requires this as M-mode uses flat addressing and the kernel
+# memory must be mapped in order to share memory between the kernel and
+# different user tasks which reside in virtual memory.
+
+config ARCH_USE_S_MODE
+	bool "Run the NuttX kernel in S-mode"
+	default n
+	depends on ARCH_HAVE_S_MODE && BUILD_KERNEL && ARCH_USE_MMU
+	---help---
+		Most of the RISC-V implementations run in M-mode (flat addressing)
+		and/or U-mode (in case of separate kernel-/userspaces). This provides
+		an option to run the kernel in S-mode, if the target supports it.
+
 # MPU has certain architecture dependent configurations, which are presented
 # here. Default is that the full RISC-V PMP specification is supported.
 

arch/risc-v/include/csr.h

@@ -299,13 +299,27 @@
 
 /* In mstatus register */
 
+#define MSTATUS_UIE       (0x1 << 0)  /* User Interrupt Enable */
+#define MSTATUS_SIE       (0x1 << 1)  /* Supervisor Interrupt Enable */
 #define MSTATUS_MIE       (0x1 << 3)  /* Machine Interrupt Enable */
+#define MSTATUS_SPIE      (0x1 << 5)  /* Supervisor Previous Interrupt Enable */
 #define MSTATUS_MPIE      (0x1 << 7)  /* Machine Previous Interrupt Enable */
+#define MSTATUS_SPPU      (0x0 << 8)  /* Supervisor Previous Privilege (u-mode) */
+#define MSTATUS_SPPS      (0x1 << 8)  /* Supervisor Previous Privilege (s-mode) */
+#define MSTATUS_MPPU      (0x0 << 11) /* Machine Previous Privilege (u-mode) */
+#define MSTATUS_MPPS      (0x1 << 11) /* Machine Previous Privilege (s-mode) */
 #define MSTATUS_MPPM      (0x3 << 11) /* Machine Previous Privilege (m-mode) */
+#define MSTATUS_MPP_MASK  (0x3 << 11)
 #define MSTATUS_FS        (0x3 << 13) /* Machine Floating-point Status */
 #define MSTATUS_FS_INIT   (0x1 << 13)
 #define MSTATUS_FS_CLEAN  (0x2 << 13)
 #define MSTATUS_FS_DIRTY  (0x3 << 13)
+#define MSTATUS_MPRV      (0x1 << 17) /* Modify Privilege */
+#define MSTATUS_SUM       (0x1 << 18) /* S mode access to U mode memory */
+#define MSTATUS_MXR       (0x1 << 19) /* Make executable / readable */
+#define MSTATUS_TVM       (0x1 << 20) /* Trap access to satp from S mode */
+#define MSTATUS_TW        (0x1 << 21) /* Trap WFI instruction from S mode */
+#define MSTATUS_TSR       (0x1 << 22) /* Trap supervisor return (sret) */
 
 /* Mask of preserved bits for mstatus */
 
@@ -317,15 +331,47 @@
 
 /* In mie (machine interrupt enable) register */
 
+#define MIE_SSIE      (0x1 << 1)  /* Supervisor Software Interrupt Enable */
 #define MIE_MSIE      (0x1 << 3)  /* Machine Software Interrupt Enable */
+#define MIE_STIE      (0x1 << 5)  /* Supervisor Timer Interrupt Enable */
 #define MIE_MTIE      (0x1 << 7)  /* Machine Timer Interrupt Enable */
+#define MIE_SEIE      (0x1 << 9)  /* Supervisor External Interrupt Enable */
 #define MIE_MEIE      (0x1 << 11) /* Machine External Interrupt Enable */
 
 /* In mip (machine interrupt pending) register */
 
-#define MIP_MTIP      (0x1 << 7)
+#define MIP_SSIP        (0x1 << 1)
+#define MIP_STIP        (0x1 << 5)
+#define MIP_MTIP        (0x1 << 7)
+#define MIP_SEIP        (0x1 << 9)
 
-#define CSR_STR(csr) #csr
+/* In sstatus register (which is a view of mstatus) */
+
+#define SSTATUS_SIE         MSTATUS_SIE
+#define SSTATUS_SPIE        MSTATUS_SPIE
+#define SSTATUS_SPPU        MSTATUS_SPPU
+#define SSTATUS_SPPS        MSTATUS_SPPS
+#define SSTATUS_FS          MSTATUS_FS
+#define SSTATUS_FS_INIT     MSTATUS_FS_INIT
+#define SSTATUS_FS_CLEAN    MSTATUS_FS_CLEAN
+#define SSTATUS_FS_DIRTY    MSTATUS_FS_DIRTY
+#define SSTATUS_SUM         MSTATUS_SUM
+#define SSTATUS_MXR         MSTATUS_MXR
+
+/* In sie register (which is a view of mie) */
+
+#define SIE_SSIE            MIE_SSIE
+#define SIE_STIE            MIE_STIE
+#define SIE_SEIE            MIE_SEIE
+
+/* In sip register (which is a view of mip) */
+
+#define SIP_SSIP            MIP_SSIP
+#define SIP_STIP            MIP_STIP
+#define SIP_SEIP            MIP_SEIP
+
+#define CSR_STR(csr)        #csr
+#define CSR_XSTR(str)       CSR_STR(str)
 
 #define READ_CSR(reg) \
   ({ \
@@ -359,8 +405,8 @@
 /* In pmpcfg (PMP configuration) register */
 
 #define PMPCFG_R        (1 << 0)  /* readable ? */
-#define PMPCFG_W        (1 << 1)  /* writeable ? */
-#define PMPCFG_X        (1 << 2)  /* excutable ? */
+#define PMPCFG_W        (1 << 1)  /* writable ? */
+#define PMPCFG_X        (1 << 2)  /* executable ? */
 #define PMPCFG_RWX_MASK (7 << 0)  /* access rights mask */
 #define PMPCFG_A_OFF    (0 << 3)  /* null region (disabled) */
 #define PMPCFG_A_TOR    (1 << 3)  /* top of range */

arch/risc-v/include/irq.h

@@ -39,6 +39,7 @@
 #include <nuttx/irq.h>
 #include <arch/csr.h>
 #include <arch/chip/irq.h>
+#include <arch/mode.h>
 #endif
 
 /****************************************************************************
@@ -50,7 +51,7 @@
 /* IRQ 0-15 : (exception:interrupt=0) */
 
 #define RISCV_IRQ_IAMISALIGNED  (0)   /* Instruction Address Misaligned */
-#define RISCV_IRQ_IAFAULT       (1)   /* Instruction Address Fault */
+#define RISCV_IRQ_IAFAULT       (1)   /* Instruction Access Fault */
 #define RISCV_IRQ_IINSTRUCTION  (2)   /* Illegal Instruction */
 #define RISCV_IRQ_BPOINT        (3)   /* Break Point */
 #define RISCV_IRQ_LAMISALIGNED  (4)   /* Load Address Misaligned */
@@ -64,7 +65,7 @@
 #define RISCV_IRQ_INSTRUCTIONPF (12)  /* Instruction page fault */
 #define RISCV_IRQ_LOADPF        (13)  /* Load page fault */
 #define RISCV_IRQ_RESERVED      (14)  /* Reserved */
-#define RISCV_IRQ_SROREPF       (15)  /* Store/AMO page fault */
+#define RISCV_IRQ_STOREPF       (15)  /* Store/AMO page fault */
 
 #define RISCV_MAX_EXCEPTION     (15)
 
@@ -99,6 +100,16 @@
 #  define CONFIG_SYS_NNEST  2
 #endif
 
+/* Amount of interrupt stacks (amount of harts) */
+
+#ifdef CONFIG_IRQ_NSTACKS
+#  define IRQ_NSTACKS       CONFIG_IRQ_NSTACKS
+#elif defined CONFIG_SMP
+#  define IRQ_NSTACKS       CONFIG_SMP_NCPUS
+#else
+#  define IRQ_NSTACKS       1
+#endif
+
 /* Processor PC */
 
 #define REG_EPC_NDX         0
@@ -472,7 +483,7 @@ struct xcpt_syscall_s
 {
   uintptr_t sysreturn;   /* The return PC */
 #ifndef CONFIG_BUILD_FLAT
-  uintptr_t int_ctx;     /* Interrupt context (i.e. mstatus) */
+  uintptr_t int_ctx;     /* Interrupt context (i.e. m-/sstatus) */
 #endif
 };
 #endif
@@ -580,9 +591,9 @@ static inline irqstate_t up_irq_save(void)
 
   __asm__ __volatile__
     (
-      "csrrc %0, mstatus, %1\n"
+      "csrrc %0, " CSR_XSTR(CSR_STATUS) ", %1\n"
       : "=r" (flags)
-      : "r"(MSTATUS_MIE)
+      : "r"(STATUS_IE)
       : "memory"
     );
 
@@ -605,7 +616,7 @@ static inline void up_irq_restore(irqstate_t flags)
 {
   __asm__ __volatile__
     (
-      "csrw mstatus, %0\n"
+      "csrw " CSR_XSTR(CSR_STATUS) ", %0\n"
       : /* no output */
       : "r" (flags)
       : "memory"

arch/risc-v/include/mode.h

@@ -0,0 +1,93 @@
+/****************************************************************************
+ * arch/risc-v/include/mode.h
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.  The
+ * ASF licenses this file to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the
+ * License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ ****************************************************************************/
+
+#ifndef __ARCH_RISCV_INCLUDE_MODE_H
+#define __ARCH_RISCV_INCLUDE_MODE_H
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <arch/csr.h>
+#include <arch/irq.h>
+
+/****************************************************************************
+ * Pre-processor Definitions
+ ****************************************************************************/
+
+#ifdef CONFIG_ARCH_USE_S_MODE
+
+/* CSR definitions */
+
+#  define CSR_STATUS        sstatus          /* Global status register */
+#  define CSR_EPC           sepc             /* Exception program counter */
+#  define CSR_IE            sie              /* Interrupt enable register */
+
+/* In status register */
+
+#  define STATUS_IE         SSTATUS_SIE      /* Global interrupt enable */
+#  define STATUS_PIE        SSTATUS_SPIE     /* Previous interrupt enable */
+#  define STATUS_PPP        SSTATUS_SPPS     /* Previous privilege */
+#  define STATUS_SUM        SSTATUS_SUM      /* Access to user memory */
+
+/* Interrupt bits */
+
+#  define IE_EIE            SIE_SEIE         /* External interrupt enable */
+#  define IE_SIE            SIE_SSIE         /* Software interrupt enable */
+#  define IE_TIE            SIE_STIE         /* Timer interrupt enable */
+
+/* External, timer and software interrupt */
+
+#  define RISCV_IRQ_EXT     RISCV_IRQ_SEXT   /* PLIC IRQ */
+#  define RISCV_IRQ_TIMER   RISCV_IRQ_STIMER /* Timer IRQ */
+#  define RISCV_IRQ_SOFT    RISCV_IRQ_SSOFT  /* SW IRQ */
+
+#else
+
+/* CSR definitions */
+
+#  define CSR_STATUS        mstatus          /* Global status register */
+#  define CSR_EPC           mepc             /* Exception program counter */
+#  define CSR_IE            mie              /* Interrupt enable register */
+
+/* In status register */
+
+#  define STATUS_IE         MSTATUS_MIE      /* Global interrupt enable */
+#  define STATUS_PIE        MSTATUS_MPIE     /* Previous interrupt enable */
+#  define STATUS_PPP        MSTATUS_MPPM     /* Previous privilege */
+#  define STATUS_SUM        0                /* Not needed in M-mode */
+
+/* Interrupt bits */
+
+#  define IE_EIE            MIE_MEIE         /* External interrupt enable */
+#  define IE_SIE            MIE_MSIE         /* Software interrupt enable */
+#  define IE_TIE            MIE_MTIE         /* Timer interrupt enable */
+
+/* External, timer and software interrupt */
+
+#  define RISCV_IRQ_EXT     RISCV_IRQ_MEXT   /* PLIC IRQ */
+#  define RISCV_IRQ_TIMER   RISCV_IRQ_MTIMER /* Timer IRQ */
+#  define RISCV_IRQ_SOFT    RISCV_IRQ_MSOFT  /* SW IRQ */
+
+#endif
+
+#endif /* __ARCH_RISCV_INCLUDE_MODE_H */