xref: /openbmc/linux/arch/arm/kernel/xscale-cp0.c (revision 303d6da1)
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 
dsp_save_state(u32 * state)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 
dsp_load_state(u32 * state)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 
dsp_do(struct notifier_block * self,unsigned long cmd,void * t)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
iwmmxt_do(struct notifier_block * self,unsigned long cmd,void * t)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 
xscale_cp_access_read(void)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 
xscale_cp_access_write(u32 value)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  */
cpu_has_iwmmxt(void)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  */
xscale_cp0_init(void)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