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Commit 1efe4ce3 authored by Stuart Menefy's avatar Stuart Menefy Committed by Paul Mundt
Browse files

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: default avatarStuart Menefy <stuart.menefy@st.com>
Signed-off-by: default avatarPaul Mundt <lethal@linux-sh.org>
parent 53ff0942

arch/sh/Kconfig

+11 −1
Original line number Diff line number Diff line
@@ -692,7 +692,7 @@ source "kernel/Kconfig.preempt" 


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 @@ config GUSA 
	  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"

arch/sh/kernel/cpu/sh3/entry.S

+23 −1
Original line number Diff line number Diff line
@@ -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 @@ ENTRY(handle_exception) 
	! 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

arch/sh/kernel/entry-common.S

+0 −19
Original line number Diff line number Diff line
@@ -176,25 +176,6 @@ work_notifysig: 
	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

arch/sh/kernel/process_32.c

+0 −19
Original line number Diff line number Diff line
@@ -322,25 +322,6 @@ struct task_struct *__switch_to(struct task_struct *prev, 
	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

arch/sh/kernel/signal_32.c

+0 −18
Original line number Diff line number Diff line
@@ -507,24 +507,6 @@ handle_signal(unsigned long sig, struct k_sigaction *ka, siginfo_t *info, 
						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 */