arch/ia64/include/asm/switch_to.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * Low-level task switching. This is based on information published in
   4  * the Processor Abstraction Layer and the System Abstraction Layer
   5  * manual.
   6  *
   7  * Copyright (C) 1998-2003 Hewlett-Packard Co
   8  *      David Mosberger-Tang <davidm@hpl.hp.com>
   9  * Copyright (C) 1999 Asit Mallick <asit.k.mallick@intel.com>
  10  * Copyright (C) 1999 Don Dugger <don.dugger@intel.com>
  11  */
  12 #ifndef _ASM_IA64_SWITCH_TO_H
  13 #define _ASM_IA64_SWITCH_TO_H
  14
  15 #include <linux/percpu.h>
  16
  17 struct task_struct;
  18
  19 /*
  20  * Context switch from one thread to another.  If the two threads have
  21  * different address spaces, schedule() has already taken care of
  22  * switching to the new address space by calling switch_mm().
  23  *
  24  * Disabling access to the fph partition and the debug-register
  25  * context switch MUST be done before calling ia64_switch_to() since a
  26  * newly created thread returns directly to
  27  * ia64_ret_from_syscall_clear_r8.
  28  */
  29 extern struct task_struct *ia64_switch_to (void *next_task);
  30
  31 extern void ia64_save_extra (struct task_struct *task);
  32 extern void ia64_load_extra (struct task_struct *task);
  33
  34 #define IA64_HAS_EXTRA_STATE(t)                                                 \
  35         ((t)->thread.flags & (IA64_THREAD_DBG_VALID|IA64_THREAD_PM_VALID))
  36
  37 #define __switch_to(prev,next,last) do {                                                         \
  38         if (IA64_HAS_EXTRA_STATE(prev))                                                          \
  39                 ia64_save_extra(prev);                                                           \
  40         if (IA64_HAS_EXTRA_STATE(next))                                                          \
  41                 ia64_load_extra(next);                                                           \
  42         ia64_psr(task_pt_regs(next))->dfh = !ia64_is_local_fpu_owner(next);                      \
  43         (last) = ia64_switch_to((next));                                                         \
  44 } while (0)
  45
  46 #ifdef CONFIG_SMP
  47 /*
  48  * In the SMP case, we save the fph state when context-switching away from a thread that
  49  * modified fph.  This way, when the thread gets scheduled on another CPU, the CPU can
  50  * pick up the state from task->thread.fph, avoiding the complication of having to fetch
  51  * the latest fph state from another CPU.  In other words: eager save, lazy restore.
  52  */
  53 # define switch_to(prev,next,last) do {                                         \
  54         if (ia64_psr(task_pt_regs(prev))->mfh && ia64_is_local_fpu_owner(prev)) {                               \
  55                 ia64_psr(task_pt_regs(prev))->mfh = 0;                  \
  56                 (prev)->thread.flags |= IA64_THREAD_FPH_VALID;                  \
  57                 __ia64_save_fpu((prev)->thread.fph);                            \
  58         }                                                                       \
  59         __switch_to(prev, next, last);                                          \
  60         /* "next" in old context is "current" in new context */                 \
  61         if (unlikely((current->thread.flags & IA64_THREAD_MIGRATION) &&        \
  62                      (task_cpu(current) !=                                     \
  63                                       task_thread_info(current)->last_cpu))) { \
  64                 task_thread_info(current)->last_cpu = task_cpu(current);       \
  65         }                                                                      \
  66 } while (0)
  67 #else
  68 # define switch_to(prev,next,last)      __switch_to(prev, next, last)
  69 #endif
  70
  71 #endif /* _ASM_IA64_SWITCH_TO_H */