riscv: syscall SYS_switch_context and SYS_restore_context use 0 para

reason:
simplify context switch
sys_call0(SYS_switch_context)
sys_call0(SYS_restore_context)

size nuttx
before
   text    data     bss     dec     hex filename
 148021     921   26944  175886   2af0e nuttx

after
   text    data     bss     dec     hex filename
 147995     921   26928  175844   2aee4 nuttx

size reduce -42

Signed-off-by: hujun5 <hujun5@xiaomi.com>

arch/risc-v/include/syscall.h

@@ -65,14 +65,14 @@
 
 /* SYS call 1:
  *
- * void riscv_fullcontextrestore(uintptr_t *restoreregs) noreturn_function;
+ * void riscv_fullcontextrestore() noreturn_function;
  */
 
 #define SYS_restore_context       (1)
 
 /* SYS call 2:
  *
- * void riscv_switchcontext(uintptr_t **saveregs, uintptr_t *restoreregs);
+ * void riscv_switchcontext();
  */
 
 #define SYS_switch_context        (2)

arch/risc-v/src/common/riscv_exit.c

@@ -54,25 +54,17 @@
 
 void up_exit(int status)
 {
-  struct tcb_s *tcb = this_task();
-
   /* Destroy the task at the head of the ready to run list. */
 
   nxtask_exit();
 
-  /* Now, perform the context switch to the new ready-to-run task at the
-   * head of the list.
-   */
-
-  tcb = this_task();
-
   /* Scheduler parameters will update inside syscall */
 
   g_running_tasks[this_cpu()] = NULL;
 
   /* Then switch contexts */
 
-  riscv_fullcontextrestore(tcb);
+  riscv_fullcontextrestore();
 
   /* riscv_fullcontextrestore() should not return but could if the software
    * interrupts are disabled.

arch/risc-v/src/common/riscv_internal.h

@@ -486,36 +486,37 @@ void riscv_jump_to_user(uintptr_t entry, uintreg_t a0, uintreg_t a1,
  * Name: riscv_fullcontextrestore
  *
  * Description:
- *   Restores the full context of the next task.
+ *   Restores the full context.
- *
- * Parameters:
- *   next - Pointer to the next task control block.
  *
  * Returned Value:
  *   None
  *
  ****************************************************************************/
 
-#define riscv_fullcontextrestore(next) \
+#define riscv_fullcontextrestore()    \
-  sys_call1(SYS_restore_context, (uintptr_t)next)
+  do                                  \
+    {                                 \
+      sys_call0(SYS_restore_context); \
+    }                                 \
+  while (1)
 
 /****************************************************************************
  * Name: riscv_switchcontext
  *
  * Description:
- *   Switches the context from the previous task to the next task.
+ *   Switches the context.
- *
- * Parameters:
- *   prev - Pointer to the previous task control block.
- *   next - Pointer to the next task control block.
  *
  * Returned Value:
  *   None
  *
  ****************************************************************************/
 
-#define riscv_switchcontext(prev, next) \
+#define riscv_switchcontext()        \
-  sys_call2(SYS_switch_context, (uintptr_t)prev, (uintptr_t)next)
+  do                                 \
+    {                                \
+      sys_call0(SYS_switch_context); \
+    }                                \
+  while (0)
 
 #undef EXTERN
 #ifdef __cplusplus

arch/risc-v/src/common/riscv_sigdeliver.c

@@ -167,5 +167,5 @@ retry:
   g_running_tasks[this_cpu()] = NULL;
 
   rtcb->xcp.regs = regs;
-  riscv_fullcontextrestore(rtcb);
+  riscv_fullcontextrestore();
 }

arch/risc-v/src/common/riscv_swint.c

@@ -148,7 +148,8 @@ uintptr_t dispatch_syscall(unsigned int nbr, uintptr_t parm1,
 int riscv_swint(int irq, void *context, void *arg)
 {
   uintreg_t *regs = (uintreg_t *)context;
-  uintreg_t *new_regs = regs;
+  struct tcb_s *tcb = this_task();
+  int cpu = this_cpu();
 
   /* Software interrupt 0 is invoked with REG_A0 (REG_X10) = system call
    * command and REG_A1-6 = variable number of
@@ -164,51 +165,18 @@ int riscv_swint(int irq, void *context, void *arg)
 
   switch (regs[REG_A0])
     {
-      /* A0=SYS_restore_context: This a restore context command:
-       *
-       * void
-       * void riscv_fullcontextrestore(struct tcb_s *prev) noreturn_function;
-       *
-       * At this point, the following values are saved in context:
-       *
-       *   A0 = SYS_restore_context
-       *   A1 = next
-       */
-
       case SYS_restore_context:
         {
-          struct tcb_s *next = (struct tcb_s *)(uintptr_t)regs[REG_A1];
+          riscv_restorecontext(tcb);
-
+          restore_critical_section(tcb, cpu);
-          DEBUGASSERT(regs[REG_A1] != 0);
-          new_regs = next->xcp.regs;
-          riscv_restorecontext(next);
         }
         break;
 
-      /* A0=SYS_switch_context: This a switch context command:
-       *
-       * void
-       * riscv_switchcontext(struct tcb_s *prev, struct tcb_s *next);
-       *
-       * At this point, the following values are saved in context:
-       *
-       *   A0 = SYS_switch_context
-       *   A1 = prev
-       *   A2 = next
-       *
-       * In this case, we save the context registers to the save register
-       * area referenced by the saved contents of R5.
-       */
-
       case SYS_switch_context:
         {
-          struct tcb_s *prev = (struct tcb_s *)(uintptr_t)regs[REG_A1];
+          riscv_savecontext(g_running_tasks[cpu]);
-          struct tcb_s *next = (struct tcb_s *)(uintptr_t)regs[REG_A2];
+          riscv_restorecontext(tcb);
-
+          restore_critical_section(tcb, cpu);
-          DEBUGASSERT(regs[REG_A1] != 0 && regs[REG_A2] != 0);
-          riscv_savecontext(prev);
-          new_regs = next->xcp.regs;
-          riscv_restorecontext(next);
         }
         break;
 
@@ -342,21 +310,17 @@ int riscv_swint(int irq, void *context, void *arg)
    * switch
    */
 
-  if (regs != new_regs)
-    {
-      restore_critical_section(this_task(), this_cpu());
-
 #ifdef CONFIG_DEBUG_SYSCALL_INFO
+  if (cmd <= SYS_switch_context)
+    {
       svcinfo("SWInt Return: Context switch!\n");
-      up_dump_register(new_regs);
+      up_dump_register(tcb.xcp.regs);
-#endif
     }
   else
     {
-#ifdef CONFIG_DEBUG_SYSCALL_INFO
       svcinfo("SWInt Return: %" PRIxPTR "\n", regs[REG_A0]);
-#endif
     }
+#endif
 
   return OK;
 }

arch/risc-v/src/common/riscv_switchcontext.c

@@ -80,7 +80,7 @@ void up_switch_context(struct tcb_s *tcb, struct tcb_s *rtcb)
     {
       /* Then switch contexts */
 
-      riscv_switchcontext(rtcb, tcb);
+      riscv_switchcontext();
 
       /* riscv_switchcontext forces a context switch to the task at the
        * head of the ready-to-run list.  It does not 'return' in the