powerpc/rtas: Add rtas_call_unlocked()

Most users of RTAS (Run-Time Abstraction Services) use rtas_call(),
which deals with locking as well as endian handling.

However we have two users outside of rtas.c that can't use rtas_call()
because they have different locking requirements.

The hotplug CPU code can't take the RTAS lock because the CPU would go
offline with the lock held and no other CPUs would be able to call RTAS
until the CPU came back online.

The xmon code doesn't want to take the lock because it would risk dead
locking when we are trying to recover from a crash.

Both sites required multiple patches when we added little endian
support, proving that programmers can't do endian right.

Although that ship has sailed, we can still clean the code up by
providing an unlocked version of rtas_call() which avoids the need to
open code the logic elsewhere.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/rtas.h

@@ -338,6 +338,8 @@ extern void enter_rtas(unsigned long);
 extern int rtas_token(const char *service);
 extern int rtas_service_present(const char *service);
 extern int rtas_call(int token, int, int, int *, ...);
+void rtas_call_unlocked(struct rtas_args *args, int token, int nargs,
+			int nret, ...);
 extern void rtas_restart(char *cmd);
 extern void rtas_power_off(void);
 extern void rtas_halt(void);

arch/powerpc/kernel/rtas.c

@@ -418,6 +418,36 @@ static char *__fetch_rtas_last_error(char *altbuf)
 #define get_errorlog_buffer()		NULL
 #endif
 
+
+static void
+va_rtas_call_unlocked(struct rtas_args *args, int token, int nargs, int nret,
+		      va_list list)
+{
+	int i;
+
+	args->token = cpu_to_be32(token);
+	args->nargs = cpu_to_be32(nargs);
+	args->nret  = cpu_to_be32(nret);
+	args->rets  = &(args->args[nargs]);
+
+	for (i = 0; i < nargs; ++i)
+		args->args[i] = cpu_to_be32(va_arg(list, __u32));
+
+	for (i = 0; i < nret; ++i)
+		args->rets[i] = 0;
+
+	enter_rtas(__pa(args));
+}
+
+void rtas_call_unlocked(struct rtas_args *args, int token, int nargs, int nret, ...)
+{
+	va_list list;
+
+	va_start(list, nret);
+	va_rtas_call_unlocked(args, token, nargs, nret, list);
+	va_end(list);
+}
+
 int rtas_call(int token, int nargs, int nret, int *outputs, ...)
 {
 	va_list list;
@@ -431,22 +461,14 @@ int rtas_call(int token, int nargs, int nret, int *outputs, ...)
 		return -1;
 
 	s = lock_rtas();
+
+	/* We use the global rtas args buffer */
 	rtas_args = &rtas.args;
 
-	rtas_args->token = cpu_to_be32(token);
-	rtas_args->nargs = cpu_to_be32(nargs);
-	rtas_args->nret  = cpu_to_be32(nret);
-	rtas_args->rets  = &(rtas_args->args[nargs]);
 	va_start(list, outputs);
-	for (i = 0; i < nargs; ++i)
-		rtas_args->args[i] = cpu_to_be32(va_arg(list, __u32));
+	va_rtas_call_unlocked(rtas_args, token, nargs, nret, list);
 	va_end(list);
 
-	for (i = 0; i < nret; ++i)
-		rtas_args->rets[i] = 0;
-
-	enter_rtas(__pa(rtas_args));
-
 	/* A -1 return code indicates that the last command couldn't
 	   be completed due to a hardware error. */
 	if (be32_to_cpu(rtas_args->rets[0]) == -1)