sh: GUSA atomic rollback support.
This implements kernel-level atomic rollback built on top of gUSA,
as an alternative non-IRQ based atomicity method. This is generally
a faster method for platforms that are lacking the LL/SC pairs that
SH-4A and later use, and is only supportable on legacy cores.
Signed-off-by: Stuart Menefy <stuart.menefy@st.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
diff --git a/arch/sh/Kconfig b/arch/sh/Kconfig
index 2dc3b17..f645f84 100644
--- a/arch/sh/Kconfig
+++ b/arch/sh/Kconfig
@@ -692,7 +692,7 @@
config GUSA
def_bool y
- depends on !SMP
+ depends on !SMP && SUPERH32
help
This enables support for gUSA (general UserSpace Atomicity).
This is the default implementation for both UP and non-ll/sc
@@ -704,6 +704,16 @@
This should only be disabled for special cases where alternate
atomicity implementations exist.
+config GUSA_RB
+ bool "Implement atomic operations by roll-back (gRB) (EXPERIMENTAL)"
+ depends on GUSA && CPU_SH3 || (CPU_SH4 && !CPU_SH4A)
+ help
+ Enabling this option will allow the kernel to implement some
+ atomic operations using a software implemention of load-locked/
+ store-conditional (LLSC). On machines which do not have hardware
+ LLSC, this should be more efficient than the other alternative of
+ disabling insterrupts around the atomic sequence.
+
endmenu
menu "Boot options"
diff --git a/arch/sh/kernel/cpu/sh3/entry.S b/arch/sh/kernel/cpu/sh3/entry.S
index 0d12a12..4004073 100644
--- a/arch/sh/kernel/cpu/sh3/entry.S
+++ b/arch/sh/kernel/cpu/sh3/entry.S
@@ -13,8 +13,9 @@
#include <linux/linkage.h>
#include <asm/asm-offsets.h>
#include <asm/thread_info.h>
-#include <asm/cpu/mmu_context.h>
#include <asm/unistd.h>
+#include <asm/cpu/mmu_context.h>
+#include <asm/page.h>
! NOTE:
! GNU as (as of 2.9.1) changes bf/s into bt/s and bra, when the address
@@ -409,6 +410,27 @@
! Using k0, k1 for scratch registers (r0_bank1, r1_bank),
! save all registers onto stack.
!
+
+#ifdef CONFIG_GUSA
+ ! Check for roll back gRB (User and Kernel)
+ mov r15, k0
+ shll k0
+ bf/s 1f
+ shll k0
+ bf/s 1f
+ stc spc, k1
+ stc r0_bank, k0
+ cmp/hs k0, k1 ! test k1 (saved PC) >= k0 (saved r0)
+ bt/s 2f
+ stc r1_bank, k1
+
+ add #-2, k0
+ add r15, k0
+ ldc k0, spc ! PC = saved r0 + r15 - 2
+2: mov k1, r15 ! SP = r1
+1:
+#endif
+
stc ssr, k0 ! Is it from kernel space?
shll k0 ! Check MD bit (bit30) by shifting it into...
shll k0 ! ...the T bit
diff --git a/arch/sh/kernel/entry-common.S b/arch/sh/kernel/entry-common.S
index 397ac71..926b2e7 100644
--- a/arch/sh/kernel/entry-common.S
+++ b/arch/sh/kernel/entry-common.S
@@ -176,25 +176,6 @@
jmp @r1
lds r0, pr
work_resched:
-#if defined(CONFIG_GUSA) && !defined(CONFIG_PREEMPT)
- ! gUSA handling
- mov.l @(OFF_SP,r15), r0 ! get user space stack pointer
- mov r0, r1
- shll r0
- bf/s 1f
- shll r0
- bf/s 1f
- mov #OFF_PC, r0
- ! SP >= 0xc0000000 : gUSA mark
- mov.l @(r0,r15), r2 ! get user space PC (program counter)
- mov.l @(OFF_R0,r15), r3 ! end point
- cmp/hs r3, r2 ! r2 >= r3?
- bt 1f
- add r3, r1 ! rewind point #2
- mov.l r1, @(r0,r15) ! reset PC to rewind point #2
- !
-1:
-#endif
mov.l 1f, r1
jsr @r1 ! schedule
nop
diff --git a/arch/sh/kernel/process_32.c b/arch/sh/kernel/process_32.c
index b483248..9ab1926 100644
--- a/arch/sh/kernel/process_32.c
+++ b/arch/sh/kernel/process_32.c
@@ -322,25 +322,6 @@
unlazy_fpu(prev, task_pt_regs(prev));
#endif
-#if defined(CONFIG_GUSA) && defined(CONFIG_PREEMPT)
- {
- struct pt_regs *regs;
-
- preempt_disable();
- regs = task_pt_regs(prev);
- if (user_mode(regs) && regs->regs[15] >= 0xc0000000) {
- int offset = (int)regs->regs[15];
-
- /* Reset stack pointer: clear critical region mark */
- regs->regs[15] = regs->regs[1];
- if (regs->pc < regs->regs[0])
- /* Go to rewind point */
- regs->pc = regs->regs[0] + offset;
- }
- preempt_enable_no_resched();
- }
-#endif
-
#ifdef CONFIG_MMU
/*
* Restore the kernel mode register
diff --git a/arch/sh/kernel/signal_32.c b/arch/sh/kernel/signal_32.c
index ca754fd..f6b5fbf 100644
--- a/arch/sh/kernel/signal_32.c
+++ b/arch/sh/kernel/signal_32.c
@@ -507,24 +507,6 @@
ctrl_inw(regs->pc - 4));
break;
}
-#ifdef CONFIG_GUSA
- } else {
- /* gUSA handling */
- preempt_disable();
-
- if (regs->regs[15] >= 0xc0000000) {
- int offset = (int)regs->regs[15];
-
- /* Reset stack pointer: clear critical region mark */
- regs->regs[15] = regs->regs[1];
- if (regs->pc < regs->regs[0])
- /* Go to rewind point #1 */
- regs->pc = regs->regs[0] + offset -
- instruction_size(ctrl_inw(regs->pc-4));
- }
-
- preempt_enable_no_resched();
-#endif
}
/* Set up the stack frame */
