1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * linux/arch/arm/kernel/xscale-cp0.c
4 *
5 * XScale DSP and iWMMXt coprocessor context switching and handling
6 */
7
8 #include <linux/types.h>
9 #include <linux/kernel.h>
10 #include <linux/signal.h>
11 #include <linux/sched.h>
12 #include <linux/init.h>
13 #include <linux/io.h>
14 #include <asm/thread_notify.h>
15 #include <asm/cputype.h>
16
17 asm(" .arch armv5te\n");
18
19 static inline void dsp_save_state(u32 *state)
20 {
21 __asm__ __volatile__ (
22 "mrrc p0, 0, %0, %1, c0\n"
23 : "=r" (state[0]), "=r" (state[1]));
24 }
25
26 static inline void dsp_load_state(u32 *state)
27 {
28 __asm__ __volatile__ (
29 "mcrr p0, 0, %0, %1, c0\n"
30 : : "r" (state[0]), "r" (state[1]));
31 }
32
33 static int dsp_do(struct notifier_block *self, unsigned long cmd, void *t)
34 {
35 struct thread_info *thread = t;
36
37 switch (cmd) {
38 case THREAD_NOTIFY_FLUSH:
39 thread->cpu_context.extra[0] = 0;
40 thread->cpu_context.extra[1] = 0;
41 break;
42
43 case THREAD_NOTIFY_SWITCH:
44 dsp_save_state(current_thread_info()->cpu_context.extra);
45 dsp_load_state(thread->cpu_context.extra);
46 break;
47 }
48
49 return NOTIFY_DONE;
50 }
51
52 static struct notifier_block dsp_notifier_block = {
53 .notifier_call = dsp_do,
54 };
55
56
57 #ifdef CONFIG_IWMMXT
58 static int iwmmxt_do(struct notifier_block *self, unsigned long cmd, void *t)
59 {
60 struct thread_info *thread = t;
61
62 switch (cmd) {
63 case THREAD_NOTIFY_FLUSH:
64 /*
65 * flush_thread() zeroes thread->fpstate, so no need
66 * to do anything here.
67 *
68 * FALLTHROUGH: Ensure we don't try to overwrite our newly
69 * initialised state information on the first fault.
70 */
71
72 case THREAD_NOTIFY_EXIT:
73 iwmmxt_task_release(thread);
74 break;
75
76 case THREAD_NOTIFY_SWITCH:
77 iwmmxt_task_switch(thread);
78 break;
79 }
80
81 return NOTIFY_DONE;
82 }
83
84 static struct notifier_block iwmmxt_notifier_block = {
85 .notifier_call = iwmmxt_do,
86 };
87 #endif
88
89
90 static u32 __init xscale_cp_access_read(void)
91 {
92 u32 value;
93
94 __asm__ __volatile__ (
95 "mrc p15, 0, %0, c15, c1, 0\n\t"
96 : "=r" (value));
97
98 return value;
99 }
100
101 static void __init xscale_cp_access_write(u32 value)
102 {
103 u32 temp;
104
105 __asm__ __volatile__ (
106 "mcr p15, 0, %1, c15, c1, 0\n\t"
107 "mrc p15, 0, %0, c15, c1, 0\n\t"
108 "mov %0, %0\n\t"
109 "sub pc, pc, #4\n\t"
110 : "=r" (temp) : "r" (value));
111 }
112
113 /*
114 * Detect whether we have a MAC coprocessor (40 bit register) or an
115 * iWMMXt coprocessor (64 bit registers) by loading 00000100:00000000
116 * into a coprocessor register and reading it back, and checking
117 * whether the upper word survived intact.
118 */
119 static int __init cpu_has_iwmmxt(void)
120 {
121 u32 lo;
122 u32 hi;
123
124 /*
125 * This sequence is interpreted by the DSP coprocessor as:
126 * mar acc0, %2, %3
127 * mra %0, %1, acc0
128 *
129 * And by the iWMMXt coprocessor as:
130 * tmcrr wR0, %2, %3
131 * tmrrc %0, %1, wR0
132 */
133 __asm__ __volatile__ (
134 "mcrr p0, 0, %2, %3, c0\n"
135 "mrrc p0, 0, %0, %1, c0\n"
136 : "=r" (lo), "=r" (hi)
137 : "r" (0), "r" (0x100));
138
139 return !!hi;
140 }
141
142
143 /*
144 * If we detect that the CPU has iWMMXt (and CONFIG_IWMMXT=y), we
145 * disable CP0/CP1 on boot, and let call_fpe() and the iWMMXt lazy
146 * switch code handle iWMMXt context switching. If on the other
147 * hand the CPU has a DSP coprocessor, we keep access to CP0 enabled
148 * all the time, and save/restore acc0 on context switch in non-lazy
149 * fashion.
150 */
151 static int __init xscale_cp0_init(void)
152 {
153 u32 cp_access;
154
155 /* do not attempt to probe iwmmxt on non-xscale family CPUs */
156 if (!cpu_is_xscale_family())
157 return 0;
158
159 cp_access = xscale_cp_access_read() & ~3;
160 xscale_cp_access_write(cp_access | 1);
161
162 if (cpu_has_iwmmxt()) {
163 #ifndef CONFIG_IWMMXT
164 pr_warn("CAUTION: XScale iWMMXt coprocessor detected, but kernel support is missing.\n");
165 #else
166 pr_info("XScale iWMMXt coprocessor detected.\n");
167 elf_hwcap |= HWCAP_IWMMXT;
168 thread_register_notifier(&iwmmxt_notifier_block);
169 register_iwmmxt_undef_handler();
170 #endif
171 } else {
172 pr_info("XScale DSP coprocessor detected.\n");
173 thread_register_notifier(&dsp_notifier_block);
174 cp_access |= 1;
175 }
176
177 xscale_cp_access_write(cp_access);
178
179 return 0;
180 }
181
182 late_initcall(xscale_cp0_init);
183
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