c6x: add ret_from_kernel_thread(), simplify kernel_thread()

Signed-off-by: Mark Salter <msalter@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

2 files changed, 32 insertions, 26 deletions

diff --git a/arch/c6x/kernel/entry.S b/arch/c6x/kernel/entry.S
index 30b37e5f4a61..6e6bd9d3d9cc 100644
--- a/arch/c6x/kernel/entry.S
+++ b/arch/c6x/kernel/entry.S
@@ -400,6 +400,26 @@ ret_from_fork_2:
         STW     .D2T2   B0,*+SP(REGS_A4+8)
 ENDPROC(ret_from_fork)
 
+ENTRY(ret_from_kernel_thread)
+#ifdef CONFIG_C6X_BIG_KERNEL
+        MVKL    .S1     schedule_tail,A0
+        MVKH    .S1     schedule_tail,A0
+        B       .S2X    A0
+#else
+        B       .S2     schedule_tail
+#endif
+        LDW     .D2T2   *+SP(REGS_A0+8),B10 /* get fn  */
+        ADDKPC  .S2     0f,B3,3
+0:
+        B       .S2     B10                /* call fn */
+        LDW     .D2T1   *+SP(REGS_A1+8),A4 /* get arg */
+        MVKL    .S2     sys_exit,B11
+        MVKH    .S2     sys_exit,B11
+        ADDKPC  .S2     0f,B3,1
+0:
+        BNOP    .S2     B11,5   /* jump to sys_exit */
+ENDPROC(ret_from_kernel_thread)
+
         ;;
         ;; These are the interrupt handlers, responsible for calling __do_IRQ()
         ;; int6 is used for syscalls (see _system_call entry)
diff --git a/arch/c6x/kernel/process.c b/arch/c6x/kernel/process.c
index 45e924a636a0..d2ffc9bdaba1 100644
--- a/arch/c6x/kernel/process.c
+++ b/arch/c6x/kernel/process.c
@@ -25,6 +25,7 @@ void	(*c6x_restart)(void);
 void    (*c6x_halt)(void);
 
 extern asmlinkage void ret_from_fork(void);
+extern asmlinkage void ret_from_kernel_thread(void);
 
 /*
  * power off function, if any
@@ -103,36 +104,21 @@ void machine_power_off(void)
         halt_loop();
 }
 
-static void kernel_thread_helper(int dummy, void *arg, int (*fn)(void *))
-{
-        do_exit(fn(arg));
-}
-
 /*
  * Create a kernel thread
  */
 int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags)
 {
-        struct pt_regs regs;
-
-        /*
-         * copy_thread sets a4 to zero (child return from fork)
-         * so we can't just set things up to directly return to
-         * fn.
-         */
-        memset(&regs, 0, sizeof(regs));
-        regs.b4 = (unsigned long) arg;
-        regs.a6 = (unsigned long) fn;
-        regs.pc = (unsigned long) kernel_thread_helper;
-        local_save_flags(regs.csr);
-        regs.csr |= 1;
-        regs.tsr = 5; /* Set GEE and GIE in TSR */
+        struct pt_regs regs = {
+                .a0 = (unsigned long)fn,
+                .a1 = (unsigned long)arg,
+                .tsr = 0, /* kernel mode */
+        };
 
         /* Ok, create the new process.. */
         return do_fork(flags | CLONE_VM | CLONE_UNTRACED, -1, &regs,
                        0, NULL, NULL);
 }
-EXPORT_SYMBOL(kernel_thread);
 
 void flush_thread(void)
 {
@@ -192,21 +178,21 @@ int copy_thread(unsigned long clone_flags, unsigned long usp,
         childregs = task_pt_regs(p);
 
         *childregs = *regs;
-        childregs->a4 = 0;
 
-        if (usp == -1)
+        if (usp == -1) {
                 /* case of  __kernel_thread: we return to supervisor space */
                 childregs->sp = (unsigned long)(childregs + 1);
-        else
+                p->thread.pc = (unsigned long) ret_from_kernel_thread;
+        } else {
                 /* Otherwise use the given stack */
                 childregs->sp = usp;
+                p->thread.pc = (unsigned long) ret_from_fork;
+        }
 
         /* Set usp/ksp */
         p->thread.usp = childregs->sp;
-        /* switch_to uses stack to save/restore 14 callee-saved regs */
         thread_saved_ksp(p) = (unsigned long)childregs - 8;
-        p->thread.pc = (unsigned int) ret_from_fork;
-        p->thread.wchan = (unsigned long) ret_from_fork;
+        p->thread.wchan = p->thread.pc;
 #ifdef __DSBT__
         {
                 unsigned long dp;