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 #endif 170 } else { 171 pr_info("XScale DSP coprocessor detected.\n"); 172 thread_register_notifier(&dsp_notifier_block); 173 cp_access |= 1; 174 } 175 176 xscale_cp_access_write(cp_access); 177 178 return 0; 179 } 180 181 late_initcall(xscale_cp0_init); 182