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1 /*
2 * linux/arch/arm/kernel/xscale-cp0.c
3 *
4 * XScale DSP and iWMMXt coprocessor context switching and handling
5 *
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License version 2 as
8 * published by the Free Software Foundation.
9 */
10
11 #include <linux/module.h>
12 #include <linux/types.h>
13 #include <linux/kernel.h>
14 #include <linux/signal.h>
15 #include <linux/sched.h>
16 #include <linux/init.h>
17 #include <linux/io.h>
18 #include <asm/thread_notify.h>
19
20 static inline void dsp_save_state(u32 *state)
21 {
22 __asm__ __volatile__ (
23 "mrrc p0, 0, %0, %1, c0\n"
24 : "=r" (state[0]), "=r" (state[1]));
25 }
26
27 static inline void dsp_load_state(u32 *state)
28 {
29 __asm__ __volatile__ (
30 "mcrr p0, 0, %0, %1, c0\n"
31 : : "r" (state[0]), "r" (state[1]));
32 }
33
34 static int dsp_do(struct notifier_block *self, unsigned long cmd, void *t)
35 {
36 struct thread_info *thread = t;
37
38 switch (cmd) {
39 case THREAD_NOTIFY_FLUSH:
40 thread->cpu_context.extra[0] = 0;
41 thread->cpu_context.extra[1] = 0;
42 break;
43
44 case THREAD_NOTIFY_SWITCH:
45 dsp_save_state(current_thread_info()->cpu_context.extra);
46 dsp_load_state(thread->cpu_context.extra);
47 break;
48 }
49
50 return NOTIFY_DONE;
51 }
52
53 static struct notifier_block dsp_notifier_block = {
54 .notifier_call = dsp_do,
55 };
56
57
58 #ifdef CONFIG_IWMMXT
59 static int iwmmxt_do(struct notifier_block *self, unsigned long cmd, void *t)
60 {
61 struct thread_info *thread = t;
62
63 switch (cmd) {
64 case THREAD_NOTIFY_FLUSH:
65 /*
66 * flush_thread() zeroes thread->fpstate, so no need
67 * to do anything here.
68 *
69 * FALLTHROUGH: Ensure we don't try to overwrite our newly
70 * initialised state information on the first fault.
71 */
72
73 case THREAD_NOTIFY_EXIT:
74 iwmmxt_task_release(thread);
75 break;
76
77 case THREAD_NOTIFY_SWITCH:
78 iwmmxt_task_switch(thread);
79 break;
80 }
81
82 return NOTIFY_DONE;
83 }
84
85 static struct notifier_block iwmmxt_notifier_block = {
86 .notifier_call = iwmmxt_do,
87 };
88 #endif
89
90
91 static u32 __init xscale_cp_access_read(void)
92 {
93 u32 value;
94
95 __asm__ __volatile__ (
96 "mrc p15, 0, %0, c15, c1, 0\n\t"
97 : "=r" (value));
98
99 return value;
100 }
101
102 static void __init xscale_cp_access_write(u32 value)
103 {
104 u32 temp;
105
106 __asm__ __volatile__ (
107 "mcr p15, 0, %1, c15, c1, 0\n\t"
108 "mrc p15, 0, %0, c15, c1, 0\n\t"
109 "mov %0, %0\n\t"
110 "sub pc, pc, #4\n\t"
111 : "=r" (temp) : "r" (value));
112 }
113
114 /*
115 * Detect whether we have a MAC coprocessor (40 bit register) or an
116 * iWMMXt coprocessor (64 bit registers) by loading 00000100:00000000
117 * into a coprocessor register and reading it back, and checking
118 * whether the upper word survived intact.
119 */
120 static int __init cpu_has_iwmmxt(void)
121 {
122 u32 lo;
123 u32 hi;
124
125 /*
126 * This sequence is interpreted by the DSP coprocessor as:
127 * mar acc0, %2, %3
128 * mra %0, %1, acc0
129 *
130 * And by the iWMMXt coprocessor as:
131 * tmcrr wR0, %2, %3
132 * tmrrc %0, %1, wR0
133 */
134 __asm__ __volatile__ (
135 "mcrr p0, 0, %2, %3, c0\n"
136 "mrrc p0, 0, %0, %1, c0\n"
137 : "=r" (lo), "=r" (hi)
138 : "r" (0), "r" (0x100));
139
140 return !!hi;
141 }
142
143
144 /*
145 * If we detect that the CPU has iWMMXt (and CONFIG_IWMMXT=y), we
146 * disable CP0/CP1 on boot, and let call_fpe() and the iWMMXt lazy
147 * switch code handle iWMMXt context switching. If on the other
148 * hand the CPU has a DSP coprocessor, we keep access to CP0 enabled
149 * all the time, and save/restore acc0 on context switch in non-lazy
150 * fashion.
151 */
152 static int __init xscale_cp0_init(void)
153 {
154 u32 cp_access;
155
156 cp_access = xscale_cp_access_read() & ~3;
157 xscale_cp_access_write(cp_access | 1);
158
159 if (cpu_has_iwmmxt()) {
160 #ifndef CONFIG_IWMMXT
161 printk(KERN_WARNING "CAUTION: XScale iWMMXt coprocessor "
162 "detected, but kernel support is missing.\n");
163 #else
164 printk(KERN_INFO "XScale iWMMXt coprocessor detected.\n");
165 elf_hwcap |= HWCAP_IWMMXT;
166 thread_register_notifier(&iwmmxt_notifier_block);
167 #endif
168 } else {
169 printk(KERN_INFO "XScale DSP coprocessor detected.\n");
170 thread_register_notifier(&dsp_notifier_block);
171 cp_access |= 1;
172 }
173
174 xscale_cp_access_write(cp_access);
175
176 return 0;
177 }
178
179 late_initcall(xscale_cp0_init);