arch/h8300/include/asm/switch_to.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef _H8300_SWITCH_TO_H
   3 #define _H8300_SWITCH_TO_H
   4
   5 /*
   6  * switch_to(n) should switch tasks to task ptr, first checking that
   7  * ptr isn't the current task, in which case it does nothing.  This
   8  * also clears the TS-flag if the task we switched to has used the
   9  * math co-processor latest.
  10  */
  11 /*
  12  * switch_to() saves the extra registers, that are not saved
  13  * automatically by SAVE_SWITCH_STACK in resume(), ie. d0-d5 and
  14  * a0-a1. Some of these are used by schedule() and its predecessors
  15  * and so we might get see unexpected behaviors when a task returns
  16  * with unexpected register values.
  17  *
  18  * syscall stores these registers itself and none of them are used
  19  * by syscall after the function in the syscall has been called.
  20  *
  21  * Beware that resume now expects *next to be in d1 and the offset of
  22  * tss to be in a1. This saves a few instructions as we no longer have
  23  * to push them onto the stack and read them back right after.
  24  *
  25  * 02/17/96 - Jes Sorensen (jds@kom.auc.dk)
  26  *
  27  * Changed 96/09/19 by Andreas Schwab
  28  * pass prev in a0, next in a1, offset of tss in d1, and whether
  29  * the mm structures are shared in d2 (to avoid atc flushing).
  30  *
  31  * H8/300 Porting 2002/09/04 Yoshinori Sato
  32  */
  33
  34 asmlinkage void resume(void);
  35 #define switch_to(prev, next, last) \
  36 do {                         \
  37         void *_last;                                        \
  38         __asm__ __volatile__(                               \
  39                 "mov.l  %1, er0\n\t"                        \
  40                 "mov.l  %2, er1\n\t"                        \
  41                 "mov.l  %3, er2\n\t"                        \
  42                 "jsr @_resume\n\t"                          \
  43                 "mov.l  er2,%0\n\t"                         \
  44                 : "=r" (_last)                              \
  45                 : "r" (&(prev->thread)),                    \
  46                   "r" (&(next->thread)),                    \
  47                   "g" (prev)                                \
  48                 : "cc", "er0", "er1", "er2", "er3");        \
  49         (last) = _last;                                     \
  50 } while (0)
  51
  52 #endif /* _H8300_SWITCH_TO_H */