LXR linux/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
  32void 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
  58void 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
  67void 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
  80