Index: Documentation/Configure.help
===================================================================
RCS file: /cvs/linux/Documentation/Attic/Configure.help,v
retrieving revision 1.109.2.8
diff -a -u -r1.109.2.8 Configure.help
--- Documentation/Configure.help	2002/09/11 12:44:23	1.109.2.8
+++ Documentation/Configure.help	2002/09/16 14:39:29
@@ -2337,6 +2337,20 @@
   for better performance, N if you don't know.  You must say Y here
   for multiprocessor machines.
 
+Support userspace atomic ops for MIPS2 CPUs
+CONFIG_MIPS_USERSPACE_ATOMIC_OPS
+  Say Y here if your CPU supports the MIPS2 ISA (i.e. it has
+  support for the "branch likely" instructions), but does not
+  have the LL and SC instructions which normally are required for
+  userspace atomic operations, e.g. for the NEC VR41xx CPUs.
+  Selecting this option guarantees that the value of the k1 register,
+  which is normally reserved for the kernel, is lower than
+  0x80000000 after any transition from kernel to userspace. It
+  also sets the read-only sysctl kernel.mips_userspace_atomic_ops to
+  the value "1", so that libc/libpthread can detect kernel support for
+  a fast test-and-set implementation for this kind of CPU (instead
+  of LL/SC emulation). If in doubt, say N.
+
 lld and scd instructions available
 CONFIG_CPU_HAS_LLDSCD
   Say Y here if your CPU has the lld and scd instructions, the 64-bit
Index: arch/mips/config-shared.in
===================================================================
RCS file: /cvs/linux/arch/mips/config-shared.in,v
retrieving revision 1.1.2.18
diff -a -u -r1.1.2.18 config-shared.in
--- arch/mips/config-shared.in	2002/09/11 12:44:28	1.1.2.18
+++ arch/mips/config-shared.in	2002/09/16 14:39:31
@@ -513,6 +513,9 @@
 dep_bool 'Override CPU Options' CONFIG_CPU_ADVANCED $CONFIG_MIPS32
 if [ "$CONFIG_CPU_ADVANCED" = "y" ]; then
    bool '  ll/sc Instructions available' CONFIG_CPU_HAS_LLSC
+   if [ "$CONFIG_CPU_HAS_LLSC" = "n" ]; then
+      bool '    Support userspace atomic ops for MIPS2 CPUs' CONFIG_MIPS_USERSPACE_ATOMIC_OPS
+   fi
    bool '  lld/scd Instructions available' CONFIG_CPU_HAS_LLDSCD
    bool '  Writeback Buffer available' CONFIG_CPU_HAS_WB
 else
@@ -528,6 +531,11 @@
 	 define_bool CONFIG_CPU_HAS_LLDSCD n
 	 define_bool CONFIG_CPU_HAS_WB n
       fi
+      if [ "$CONFIG_CPU_VR41XX" = "y" ]; then
+         define_bool CONFIG_MIPS_USERSPACE_ATOMIC_OPS y
+      else
+         define_bool CONFIG_MIPS_USERSPACE_ATOMIC_OPS n
+      fi
    else
       if [ "$CONFIG_CPU_MIPS32" = "y" ]; then
 	 define_bool CONFIG_CPU_HAS_LLSC y
@@ -538,6 +546,7 @@
 	 define_bool CONFIG_CPU_HAS_LLDSCD y
 	 define_bool CONFIG_CPU_HAS_WB n
       fi
+      define_bool CONFIG_MIPS_USERSPACE_ATOMIC_OPS n
    fi
 fi
 if [ "$CONFIG_CPU_R3000" = "y" ]; then
Index: include/asm-mips/stackframe.h
===================================================================
RCS file: /cvs/linux/include/asm-mips/stackframe.h,v
retrieving revision 1.18.2.2
diff -a -u -r1.18.2.2 stackframe.h
--- include/asm-mips/stackframe.h	2002/08/05 23:53:37	1.18.2.2
+++ include/asm-mips/stackframe.h	2002/09/16 14:39:35
@@ -201,8 +201,15 @@
 		lw	$3,  PT_R3(sp);                  \
 		lw	$2,  PT_R2(sp)
 
+#ifdef CONFIG_MIPS_USERSPACE_ATOMIC_OPS
+#define CLEAR_K1 move k1,$0;
+#else
+#define CLEAR_K1
+#endif
+
 #define RESTORE_SP_AND_RET                               \
 		lw	sp,  PT_R29(sp);                 \
+		CLEAR_K1                                 \
 		.set	mips3;				 \
 		eret;					 \
 		.set	mips0
Index: include/linux/sysctl.h
===================================================================
RCS file: /cvs/linux/include/linux/sysctl.h,v
retrieving revision 1.44.2.3
diff -a -u -r1.44.2.3 sysctl.h
--- include/linux/sysctl.h	2002/09/11 12:45:40	1.44.2.3
+++ include/linux/sysctl.h	2002/09/16 14:39:35
@@ -124,6 +124,7 @@
 	KERN_CORE_USES_PID=52,		/* int: use core or core.%pid */
 	KERN_TAINTED=53,	/* int: various kernel tainted flags */
 	KERN_CADPID=54,		/* int: PID of the process to notify on CAD */
+	KERN_MIPS_USERSPACE_ATOMIC_OPS=55, /* int: kernel supports atomicity w/o LL/SC */
 };
 
 
Index: kernel/sysctl.c
===================================================================
RCS file: /cvs/linux/kernel/sysctl.c,v
retrieving revision 1.46.2.4
diff -a -u -r1.46.2.4 sysctl.c
--- kernel/sysctl.c	2002/09/10 15:32:56	1.46.2.4
+++ kernel/sysctl.c	2002/09/16 14:39:36
@@ -96,6 +96,10 @@
 extern int acct_parm[];
 #endif
 
+#ifdef CONFIG_MIPS_USERSPACE_ATOMIC_OPS
+static int mips_userspace_atomic_ops = 1;
+#endif
+
 extern int pgt_cache_water[];
 
 static int parse_table(int *, int, void *, size_t *, void *, size_t,
@@ -255,6 +259,10 @@
 #endif
 	{KERN_S390_USER_DEBUG_LOGGING,"userprocess_debug",
 	 &sysctl_userprocess_debug,sizeof(int),0644,NULL,&proc_dointvec},
+#endif
+#ifdef CONFIG_MIPS_USERSPACE_ATOMIC_OPS
+	{KERN_MIPS_USERSPACE_ATOMIC_OPS, "mips_userspace_atomic_ops",
+	 &mips_userspace_atomic_ops, sizeof(int), 0444, NULL, &proc_dointvec},
 #endif
 	{0}
 };