xtensa: initialize atomctl SR

In order to use S32C1I instruction on cores with ATOMCTL SR the register
must be properly initialized.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Chris Zankel <chris@zankel.net>

Documentation/xtensa/atomctl.txt

@@ -0,0 +1,44 @@
+We Have Atomic Operation Control (ATOMCTL) Register.
+This register determines the effect of using a S32C1I instruction
+with various combinations of:
+
+     1. With and without an Coherent Cache Controller which
+        can do Atomic Transactions to the memory internally.
+
+     2. With and without An Intelligent Memory Controller which
+        can do Atomic Transactions itself.
+
+The Core comes up with a default value of for the three types of cache ops:
+
+      0x28: (WB: Internal, WT: Internal, BY:Exception)
+
+On the FPGA Cards we typically simulate an Intelligent Memory controller
+which can implement  RCW transactions. For FPGA cards with an External
+Memory controller we let it to the atomic operations internally while
+doing a Cached (WB) transaction and use the Memory RCW for un-cached
+operations.
+
+For systems without an coherent cache controller, non-MX, we always
+use the memory controllers RCW, thought non-MX controlers likely
+support the Internal Operation.
+
+CUSTOMER-WARNING:
+   Virtually all customers buy their memory controllers from vendors that
+   don't support atomic RCW memory transactions and will likely want to
+   configure this register to not use RCW.
+
+Developers might find using RCW in Bypass mode convenient when testing
+with the cache being bypassed; for example studying cache alias problems.
+
+See Section 4.3.12.4 of ISA; Bits:
+
+                             WB     WT      BY
+                           5   4 | 3   2 | 1   0
+  2 Bit
+  Field
+  Values     WB - Write Back         WT - Write Thru         BY - Bypass
+---------    ---------------         -----------------     ----------------
+    0        Exception               Exception               Exception
+    1        RCW Transaction         RCW Transaction         RCW Transaction
+    2        Internal Operation      Exception               Reserved
+    3        Reserved                Reserved                Reserved

arch/xtensa/include/asm/initialize_mmu.h

@@ -0,0 +1,55 @@
+/*
+ * arch/xtensa/include/asm/initialize_mmu.h
+ *
+ * Initializes MMU:
+ *
+ *      For the new V3 MMU we remap the TLB from virtual == physical
+ *      to the standard Linux mapping used in earlier MMU's.
+ *
+ *      The the MMU we also support a new configuration register that
+ *      specifies how the S32C1I instruction operates with the cache
+ *      controller.
+ *
+ * This file is subject to the terms and conditions of the GNU General
+ * Public License.  See the file "COPYING" in the main directory of
+ * this archive for more details.
+ *
+ * Copyright (C) 2008 - 2012 Tensilica, Inc.
+ *
+ *   Marc Gauthier <marc@tensilica.com>
+ *   Pete Delaney <piet@tensilica.com>
+ */
+
+#ifndef _XTENSA_INITIALIZE_MMU_H
+#define _XTENSA_INITIALIZE_MMU_H
+
+#ifdef __ASSEMBLY__
+
+#define XTENSA_HWVERSION_RC_2009_0 230000
+
+	.macro	initialize_mmu
+
+#if XCHAL_HAVE_S32C1I && (XCHAL_HW_MIN_VERSION >= XTENSA_HWVERSION_RC_2009_0)
+/*
+ * We Have Atomic Operation Control (ATOMCTL) Register; Initialize it.
+ * For details see Documentation/xtensa/atomctl.txt
+ */
+#if XCHAL_DCACHE_IS_COHERENT
+	movi	a3, 0x25	/* For SMP/MX -- internal for writeback,
+				 * RCW otherwise
+				 */
+#else
+	movi	a3, 0x29	/* non-MX -- Most cores use Std Memory
+				 * Controlers which usually can't use RCW
+				 */
+#endif
+	wsr	a3, atomctl
+#endif  /* XCHAL_HAVE_S32C1I &&
+	 * (XCHAL_HW_MIN_VERSION >= XTENSA_HWVERSION_RC_2009_0)
+	 */
+
+	.endm
+
+#endif /*__ASSEMBLY__*/
+
+#endif /* _XTENSA_INITIALIZE_MMU_H */

arch/xtensa/kernel/head.S

@@ -18,6 +18,7 @@
 #include <asm/processor.h>
 #include <asm/page.h>
 #include <asm/cacheasm.h>
+#include <asm/initialize_mmu.h>
 
 #include <linux/init.h>
 #include <linux/linkage.h>
@@ -155,6 +156,8 @@ ENTRY(_startup)
 
 	isync
 
+	initialize_mmu
+
 	/* Unpack data sections
 	 *
 	 * The linker script used to build the Linux kernel image