Commit c622b29d authored by Max Filippov's avatar Max Filippov Committed by Chris Zankel
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xtensa: initialize atomctl SR

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

Signed-off-by: default avatarMax Filippov <>
Signed-off-by: default avatarChris Zankel <>
parent 733536b8
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
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.
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 of ISA; Bits:
5 4 | 3 2 | 1 0
2 Bit
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
* 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 <>
* Pete Delaney <>
#ifdef __ASSEMBLY__
#define XTENSA_HWVERSION_RC_2009_0 230000
.macro initialize_mmu
* We Have Atomic Operation Control (ATOMCTL) Register; Initialize it.
* For details see Documentation/xtensa/atomctl.txt
movi a3, 0x25 /* For SMP/MX -- internal for writeback,
* RCW otherwise
movi a3, 0x29 /* non-MX -- Most cores use Std Memory
* Controlers which usually can't use RCW
wsr a3, atomctl
#endif /* XCHAL_HAVE_S32C1I &&
#endif /*__ASSEMBLY__*/
......@@ -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)
/* Unpack data sections
* The linker script used to build the Linux kernel image
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