linux/arch/arc/include/asm/entry-compact.h

/*
 * Copyright (C) 2014-15 Synopsys, Inc. (www.synopsys.com)
 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * Vineetg: March 2009 (Supporting 2 levels of Interrupts)
 *  Stack switching code can no longer reliably rely on the fact that
 *  if we are NOT in user mode, stack is switched to kernel mode.
 *  e.g. L2 IRQ interrupted a L1 ISR which had not yet completed
 *  it's prologue including stack switching from user mode
 *
 * Vineetg: Aug 28th 2008: Bug #94984
 *  -Zero Overhead Loop Context shd be cleared when entering IRQ/EXcp/Trap
 *   Normally CPU does this automatically, however when doing FAKE rtie,
 *   we also need to explicitly do this. The problem in macros
 *   FAKE_RET_FROM_EXCPN and FAKE_RET_FROM_EXCPN_LOCK_IRQ was that this bit
 *   was being "CLEARED" rather then "SET". Actually "SET" clears ZOL context
 *
 * Vineetg: May 5th 2008
 *  -Modified CALLEE_REG save/restore macros to handle the fact that
 *      r25 contains the kernel current task ptr
 *  - Defined Stack Switching Macro to be reused in all intr/excp hdlrs
 *  - Shaved off 11 instructions from RESTORE_ALL_INT1 by using the
 *      address Write back load ld.ab instead of seperate ld/add instn
 *
 * Amit Bhor, Sameer Dhavale: Codito Technologies 2004
 */

#ifndef __ASM_ARC_ENTRY_COMPACT_H
#define __ASM_ARC_ENTRY_COMPACT_H

#include <asm/asm-offsets.h>
#include <asm/thread_info.h>	/* For THREAD_SIZE */

/*--------------------------------------------------------------
 * Switch to Kernel Mode stack if SP points to User Mode stack
 *
 * Entry   : r9 contains pre-IRQ/exception/trap status32
 * Exit    : SP is set to kernel mode stack pointer
 *           If CURR_IN_REG, r25 set to "current" task pointer
 * Clobbers: r9
 *-------------------------------------------------------------*/

.macro SWITCH_TO_KERNEL_STK

	/* User Mode when this happened ? Yes: Proceed to switch stack */
	bbit1   r9, STATUS_U_BIT, 88f

	/* OK we were already in kernel mode when this event happened, thus can
	 * assume SP is kernel mode SP. _NO_ need to do any stack switching
	 */

#ifdef CONFIG_ARC_COMPACT_IRQ_LEVELS
	/* However....
	 * If Level 2 Interrupts enabled, we may end up with a corner case:
	 * 1. User Task executing
	 * 2. L1 IRQ taken, ISR starts (CPU auto-switched to KERNEL mode)
	 * 3. But before it could switch SP from USER to KERNEL stack
	 *      a L2 IRQ "Interrupts" L1
	 * Thay way although L2 IRQ happened in Kernel mode, stack is still
	 * not switched.
	 * To handle this, we may need to switch stack even if in kernel mode
	 * provided SP has values in range of USER mode stack ( < 0x7000_0000 )
	 */
	brlo sp, VMALLOC_START, 88f

	/* TODO: vineetg:
	 * We need to be a bit more cautious here. What if a kernel bug in
	 * L1 ISR, caused SP to go whaco (some small value which looks like
	 * USER stk) and then we take L2 ISR.
	 * Above brlo alone would treat it as a valid L1-L2 sceanrio
	 * instead of shouting alound
	 * The only feasible way is to make sure this L2 happened in
	 * L1 prelogue ONLY i.e. ilink2 is less than a pre-set marker in
	 * L1 ISR before it switches stack
	 */

#endif

	/* Save Pre Intr/Exception KERNEL MODE SP on kernel stack
	 * safe-keeping not really needed, but it keeps the epilogue code
	 * (SP restore) simpler/uniform.
	 */
	b.d	66f
	mov	r9, sp

88: /*------Intr/Ecxp happened in user mode, "switch" stack ------ */

	GET_CURR_TASK_ON_CPU   r9

	/* With current tsk in r9, get it's kernel mode stack base */
	GET_TSK_STACK_BASE  r9, r9

66:
#ifdef CONFIG_ARC_CURR_IN_REG
	/*
	 * Treat r25 as scratch reg, save it on stack first
	 * Load it with current task pointer
	 */
	st	r25, [r9, -4]
	GET_CURR_TASK_ON_CPU   r25
#endif

	/* Save Pre Intr/Exception User SP on kernel stack */
	st.a    sp, [r9, -16]	; Make room for orig_r0, ECR, user_r25

	/* CAUTION:
	 * SP should be set at the very end when we are done with everything
	 * In case of 2 levels of interrupt we depend on value of SP to assume
	 * that everything else is done (loading r25 etc)
	 */

	/* set SP to point to kernel mode stack */
	mov sp, r9

	/* ----- Stack Switched to kernel Mode, Now save REG FILE ----- */

.endm

/*------------------------------------------------------------
 * "FAKE" a rtie to return from CPU Exception context
 * This is to re-enable Exceptions within exception
 * Look at EV_ProtV to see how this is actually used
 *-------------------------------------------------------------*/

.macro FAKE_RET_FROM_EXCPN

	ld  r9, [sp, PT_status32]
	bic r9, r9, (STATUS_U_MASK|STATUS_DE_MASK)
	bset  r9, r9, STATUS_L_BIT
	sr  r9, [erstatus]
	mov r9, 55f
	sr  r9, [eret]

	rtie
55:
.endm

/*--------------------------------------------------------------
 * For early Exception/ISR Prologue, a core reg is temporarily needed to
 * code the rest of prolog (stack switching). This is done by stashing
 * it to memory (non-SMP case) or SCRATCH0 Aux Reg (SMP).
 *
 * Before saving the full regfile - this reg is restored back, only
 * to be saved again on kernel mode stack, as part of pt_regs.
 *-------------------------------------------------------------*/
.macro PROLOG_FREEUP_REG	reg, mem
#ifdef CONFIG_SMP
	sr  \reg, [ARC_REG_SCRATCH_DATA0]
#else
	st  \reg, [\mem]
#endif
.endm

.macro PROLOG_RESTORE_REG	reg, mem
#ifdef CONFIG_SMP
	lr  \reg, [ARC_REG_SCRATCH_DATA0]
#else
	ld  \reg, [\mem]
#endif
.endm

/*--------------------------------------------------------------
 * Exception Entry prologue
 * -Switches stack to K mode (if not already)
 * -Saves the register file
 *
 * After this it is safe to call the "C" handlers
 *-------------------------------------------------------------*/
.macro EXCEPTION_PROLOGUE

	/* Need at least 1 reg to code the early exception prologue */
	PROLOG_FREEUP_REG r9, @ex_saved_reg1

	/* U/K mode at time of exception (stack not switched if already K) */
	lr  r9, [erstatus]

	/* ARC700 doesn't provide auto-stack switching */
	SWITCH_TO_KERNEL_STK

	lr	r9, [ecr]
	st      r9, [sp, 8]    /* ECR */
	st      r0, [sp, 4]    /* orig_r0, needed only for sys calls */

	/* Restore r9 used to code the early prologue */
	PROLOG_RESTORE_REG  r9, @ex_saved_reg1

	SAVE_R0_TO_R12
	PUSH	gp
	PUSH	fp
	PUSH	blink
	PUSHAX	eret
	PUSHAX	erstatus
	PUSH	lp_count
	PUSHAX	lp_end
	PUSHAX	lp_start
	PUSHAX	erbta
.endm

/*--------------------------------------------------------------
 * Restore all registers used by system call or Exceptions
 * SP should always be pointing to the next free stack element
 * when entering this macro.
 *
 * NOTE:
 *
 * It is recommended that lp_count/ilink1/ilink2 not be used as a dest reg
 * for memory load operations. If used in that way interrupts are deffered
 * by hardware and that is not good.
 *-------------------------------------------------------------*/
.macro EXCEPTION_EPILOGUE
	POPAX	erbta
	POPAX	lp_start
	POPAX	lp_end

	POP	r9
	mov	lp_count, r9	;LD to lp_count is not allowed

	POPAX	erstatus
	POPAX	eret
	POP	blink
	POP	fp
	POP	gp
	RESTORE_R12_TO_R0

	ld  sp, [sp] /* restore original sp */
	/* orig_r0, ECR, user_r25 skipped automatically */
.endm

/* Dummy ECR values for Interrupts */
#define event_IRQ1		0x0031abcd
#define event_IRQ2		0x0032abcd

.macro INTERRUPT_PROLOGUE  LVL

	/* free up r9 as scratchpad */
	PROLOG_FREEUP_REG r9, @int\LVL\()_saved_reg

	/* Which mode (user/kernel) was the system in when intr occured */
	lr  r9, [status32_l\LVL\()]

	SWITCH_TO_KERNEL_STK

	/* restore original r9 */
	PROLOG_RESTORE_REG  r9, @int\LVL\()_saved_reg

	/* now we are ready to save the remaining context */
	st	0x003\LVL\()abcd, [sp, 8]    /* Dummy ECR */
	st      0, [sp, 4]    /* orig_r0 , N/A for IRQ */

	SAVE_R0_TO_R12
	PUSH	gp
	PUSH	fp
	PUSH	blink
	PUSH	ilink\LVL\()
	PUSHAX	status32_l\LVL\()
	PUSH	lp_count
	PUSHAX	lp_end
	PUSHAX	lp_start
	PUSHAX	bta_l\LVL\()
.endm

/*--------------------------------------------------------------
 * Restore all registers used by interrupt handlers.
 *
 * NOTE:
 *
 * It is recommended that lp_count/ilink1/ilink2 not be used as a dest reg
 * for memory load operations. If used in that way interrupts are deffered
 * by hardware and that is not good.
 *-------------------------------------------------------------*/
.macro INTERRUPT_EPILOGUE  LVL
	POPAX	bta_l\LVL\()
	POPAX	lp_start
	POPAX	lp_end

	POP	r9
	mov	lp_count, r9	;LD to lp_count is not allowed

	POPAX	status32_l\LVL\()
	POP	ilink\LVL\()
	POP	blink
	POP	fp
	POP	gp
	RESTORE_R12_TO_R0

	ld  sp, [sp] /* restore original sp */
	/* orig_r0, ECR, user_r25 skipped automatically */
.endm

/* Get thread_info of "current" tsk */
.macro GET_CURR_THR_INFO_FROM_SP  reg
	bic \reg, sp, (THREAD_SIZE - 1)
.endm

/* Get CPU-ID of this core */
.macro  GET_CPU_ID  reg
	lr  \reg, [identity]
	lsr \reg, \reg, 8
	bmsk \reg, \reg, 7
.endm

#endif  /* __ASM_ARC_ENTRY_COMPACT_H */