arch/arc/kernel/fpu.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * fpu.c - save/restore of Floating Point Unit Registers on task switch
   4  *
   5  * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
   6  */
   7
   8 #include <linux/sched.h>
   9 #include <asm/fpu.h>
  10
  11 #ifdef CONFIG_ISA_ARCOMPACT
  12
  13 /*
  14  * To save/restore FPU regs, simplest scheme would use LR/SR insns.
  15  * However since SR serializes the pipeline, an alternate "hack" can be used
  16  * which uses the FPU Exchange insn (DEXCL) to r/w FPU regs.
  17  *
  18  * Store to 64bit dpfp1 reg from a pair of core regs:
  19  *   dexcl1 0, r1, r0  ; where r1:r0 is the 64 bit val
  20  *
  21  * Read from dpfp1 into pair of core regs (w/o clobbering dpfp1)
  22  *   mov_s    r3, 0
  23  *   daddh11  r1, r3, r3   ; get "hi" into r1 (dpfp1 unchanged)
  24  *   dexcl1   r0, r1, r3   ; get "low" into r0 (dpfp1 low clobbered)
  25  *   dexcl1    0, r1, r0   ; restore dpfp1 to orig value
  26  *
  27  * However we can tweak the read, so that read-out of outgoing task's FPU regs
  28  * and write of incoming task's regs happen in one shot. So all the work is
  29  * done before context switch
  30  */
  31
  32 void fpu_save_restore(struct task_struct *prev, struct task_struct *next)
  33 {
  34         unsigned int *saveto = &prev->thread.fpu.aux_dpfp[0].l;
  35         unsigned int *readfrom = &next->thread.fpu.aux_dpfp[0].l;
  36
  37         const unsigned int zero = 0;
  38
  39         __asm__ __volatile__(
  40                 "daddh11  %0, %2, %2\n"
  41                 "dexcl1   %1, %3, %4\n"
  42                 : "=&r" (*(saveto + 1)), /* early clobber must here */
  43                   "=&r" (*(saveto))
  44                 : "r" (zero), "r" (*(readfrom + 1)), "r" (*(readfrom))
  45         );
  46
  47         __asm__ __volatile__(
  48                 "daddh22  %0, %2, %2\n"
  49                 "dexcl2   %1, %3, %4\n"
  50                 : "=&r"(*(saveto + 3)), /* early clobber must here */
  51                   "=&r"(*(saveto + 2))
  52                 : "r" (zero), "r" (*(readfrom + 3)), "r" (*(readfrom + 2))
  53         );
  54 }
  55
  56 #else
  57
  58 void fpu_init_task(struct pt_regs *regs)
  59 {
  60         /* default rounding mode */
  61         write_aux_reg(ARC_REG_FPU_CTRL, 0x100);
  62
  63         /* set "Write enable" to allow explicit write to exception flags */
  64         write_aux_reg(ARC_REG_FPU_STATUS, 0x80000000);
  65 }
  66
  67 void fpu_save_restore(struct task_struct *prev, struct task_struct *next)
  68 {
  69         struct arc_fpu *save = &prev->thread.fpu;
  70         struct arc_fpu *restore = &next->thread.fpu;
  71
  72         save->ctrl = read_aux_reg(ARC_REG_FPU_CTRL);
  73         save->status = read_aux_reg(ARC_REG_FPU_STATUS);
  74
  75         write_aux_reg(ARC_REG_FPU_CTRL, restore->ctrl);
  76         write_aux_reg(ARC_REG_FPU_STATUS, restore->status);
  77 }
  78
  79 #endif