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 <asm/thread_notify.h>
18#include <asm/io.h>
19
20static 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
27static 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
34static 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
53static struct notifier_block dsp_notifier_block = {
54	.notifier_call	= dsp_do,
55};
56
57
58#ifdef CONFIG_IWMMXT
59static 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_RELEASE:
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
85static struct notifier_block iwmmxt_notifier_block = {
86	.notifier_call	= iwmmxt_do,
87};
88#endif
89
90
91static 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
102static 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 */
120static 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 */
152static 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
179late_initcall(xscale_cp0_init);
180