arc/kernel/ctx_sw_asm.S

0001 /* SPDX-License-Identifier: GPL-2.0-only */
0002 /*
0003  * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
0004  *
0005  * Vineetg: Aug 2009
0006  *  -Moved core context switch macro out of entry.S into this file.
0007  *  -This is the more "natural" hand written assembler
0008  */
0009
0010 #include <linux/linkage.h>
0011 #include <asm/entry.h>       /* For the SAVE_* macros */
0012 #include <asm/asm-offsets.h>
0013
0014 #define KSP_WORD_OFF    ((TASK_THREAD + THREAD_KSP) / 4)
0015
0016 ;################### Low Level Context Switch ##########################
0017
0018     .section .sched.text,"ax",@progbits
0019     .align 4
0020     .global __switch_to
0021     .type   __switch_to, @function
0022 __switch_to:
0023     CFI_STARTPROC
0024
0025     /* Save regs on kernel mode stack of task */
0026     st.a    blink, [sp, -4]
0027     st.a    fp, [sp, -4]
0028     SAVE_CALLEE_SAVED_KERNEL
0029
0030     /* Save the now KSP in task->thread.ksp */
0031 #if KSP_WORD_OFF  <= 255
0032     st.as  sp, [r0, KSP_WORD_OFF]
0033 #else
0034     /* Workaround for NR_CPUS=4k as ST.as can only take s9 offset */
0035     add2    r24, r0, KSP_WORD_OFF
0036     st  sp, [r24]
0037 #endif
0038     /*
0039     * Return last task in r0 (return reg)
0040     * On ARC, Return reg = First Arg reg = r0.
0041     * Since we already have last task in r0,
0042     * don't need to do anything special to return it
0043     */
0044
0045     /*
0046      * switch to new task, contained in r1
0047      * Temp reg r3 is required to get the ptr to store val
0048      */
0049     SET_CURR_TASK_ON_CPU  r1, r3
0050
0051     /* reload SP with kernel mode stack pointer in task->thread.ksp */
0052     ld.as  sp, [r1, (TASK_THREAD + THREAD_KSP)/4]
0053
0054     /* restore the registers */
0055     RESTORE_CALLEE_SAVED_KERNEL
0056     ld.ab   fp, [sp, 4]
0057     ld.ab   blink, [sp, 4]
0058     j       [blink]
0059
0060 END_CFI(__switch_to)