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/types.h>
  12 #include <linux/kernel.h>
  13 #include <linux/signal.h>
  14 #include <linux/sched.h>
  15 #include <linux/init.h>
  16 #include <linux/io.h>
  17 #include <asm/thread_notify.h>
  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         cp_access = xscale_cp_access_read() & ~3;
 156         xscale_cp_access_write(cp_access | 1);
 157
 158         if (cpu_has_iwmmxt()) {
 159 #ifndef CONFIG_IWMMXT
 160                 printk(KERN_WARNING "CAUTION: XScale iWMMXt coprocessor "
 161                         "detected, but kernel support is missing.\n");
 162 #else
 163                 printk(KERN_INFO "XScale iWMMXt coprocessor detected.\n");
 164                 elf_hwcap |= HWCAP_IWMMXT;
 165                 thread_register_notifier(&iwmmxt_notifier_block);
 166 #endif
 167         } else {
 168                 printk(KERN_INFO "XScale DSP coprocessor detected.\n");
 169                 thread_register_notifier(&dsp_notifier_block);
 170                 cp_access |= 1;
 171         }
 172
 173         xscale_cp_access_write(cp_access);
 174
 175         return 0;
 176 }
 177
 178 late_initcall(xscale_cp0_init);