xref: /openbmc/linux/arch/ia64/include/asm/switch_to.h (revision 31b90347)
1 /*
2  * Low-level task switching. This is based on information published in
3  * the Processor Abstraction Layer and the System Abstraction Layer
4  * manual.
5  *
6  * Copyright (C) 1998-2003 Hewlett-Packard Co
7  *	David Mosberger-Tang <davidm@hpl.hp.com>
8  * Copyright (C) 1999 Asit Mallick <asit.k.mallick@intel.com>
9  * Copyright (C) 1999 Don Dugger <don.dugger@intel.com>
10  */
11 #ifndef _ASM_IA64_SWITCH_TO_H
12 #define _ASM_IA64_SWITCH_TO_H
13 
14 #include <linux/percpu.h>
15 
16 struct task_struct;
17 
18 /*
19  * Context switch from one thread to another.  If the two threads have
20  * different address spaces, schedule() has already taken care of
21  * switching to the new address space by calling switch_mm().
22  *
23  * Disabling access to the fph partition and the debug-register
24  * context switch MUST be done before calling ia64_switch_to() since a
25  * newly created thread returns directly to
26  * ia64_ret_from_syscall_clear_r8.
27  */
28 extern struct task_struct *ia64_switch_to (void *next_task);
29 
30 extern void ia64_save_extra (struct task_struct *task);
31 extern void ia64_load_extra (struct task_struct *task);
32 
33 #ifdef CONFIG_PERFMON
34   DECLARE_PER_CPU(unsigned long, pfm_syst_info);
35 # define PERFMON_IS_SYSWIDE() (__get_cpu_var(pfm_syst_info) & 0x1)
36 #else
37 # define PERFMON_IS_SYSWIDE() (0)
38 #endif
39 
40 #define IA64_HAS_EXTRA_STATE(t)							\
41 	((t)->thread.flags & (IA64_THREAD_DBG_VALID|IA64_THREAD_PM_VALID)	\
42 	 || PERFMON_IS_SYSWIDE())
43 
44 #define __switch_to(prev,next,last) do {							 \
45 	if (IA64_HAS_EXTRA_STATE(prev))								 \
46 		ia64_save_extra(prev);								 \
47 	if (IA64_HAS_EXTRA_STATE(next))								 \
48 		ia64_load_extra(next);								 \
49 	ia64_psr(task_pt_regs(next))->dfh = !ia64_is_local_fpu_owner(next);			 \
50 	(last) = ia64_switch_to((next));							 \
51 } while (0)
52 
53 #ifdef CONFIG_SMP
54 /*
55  * In the SMP case, we save the fph state when context-switching away from a thread that
56  * modified fph.  This way, when the thread gets scheduled on another CPU, the CPU can
57  * pick up the state from task->thread.fph, avoiding the complication of having to fetch
58  * the latest fph state from another CPU.  In other words: eager save, lazy restore.
59  */
60 # define switch_to(prev,next,last) do {						\
61 	if (ia64_psr(task_pt_regs(prev))->mfh && ia64_is_local_fpu_owner(prev)) {				\
62 		ia64_psr(task_pt_regs(prev))->mfh = 0;			\
63 		(prev)->thread.flags |= IA64_THREAD_FPH_VALID;			\
64 		__ia64_save_fpu((prev)->thread.fph);				\
65 	}									\
66 	__switch_to(prev, next, last);						\
67 	/* "next" in old context is "current" in new context */			\
68 	if (unlikely((current->thread.flags & IA64_THREAD_MIGRATION) &&	       \
69 		     (task_cpu(current) !=				       \
70 		      		      task_thread_info(current)->last_cpu))) { \
71 		platform_migrate(current);				       \
72 		task_thread_info(current)->last_cpu = task_cpu(current);       \
73 	}								       \
74 } while (0)
75 #else
76 # define switch_to(prev,next,last)	__switch_to(prev, next, last)
77 #endif
78 
79 #endif /* _ASM_IA64_SWITCH_TO_H */
80