arch/arm/kernel/xscale-cp0.c

   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);