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 */
72