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xscale-cp0.c

/*
 * linux/arch/arm/kernel/xscale-cp0.c
 *
 * XScale DSP and iWMMXt coprocessor context switching and handling
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/module.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/io.h>
#include <asm/thread_notify.h>

static inline void dsp_save_state(u32 *state)
{
      __asm__ __volatile__ (
            "mrrc p0, 0, %0, %1, c0\n"
            : "=r" (state[0]), "=r" (state[1]));
}

static inline void dsp_load_state(u32 *state)
{
      __asm__ __volatile__ (
            "mcrr p0, 0, %0, %1, c0\n"
            : : "r" (state[0]), "r" (state[1]));
}

static int dsp_do(struct notifier_block *self, unsigned long cmd, void *t)
{
      struct thread_info *thread = t;

      switch (cmd) {
      case THREAD_NOTIFY_FLUSH:
            thread->cpu_context.extra[0] = 0;
            thread->cpu_context.extra[1] = 0;
            break;

      case THREAD_NOTIFY_SWITCH:
            dsp_save_state(current_thread_info()->cpu_context.extra);
            dsp_load_state(thread->cpu_context.extra);
            break;
      }

      return NOTIFY_DONE;
}

static struct notifier_block dsp_notifier_block = {
      .notifier_call    = dsp_do,
};


#ifdef CONFIG_IWMMXT
static int iwmmxt_do(struct notifier_block *self, unsigned long cmd, void *t)
{
      struct thread_info *thread = t;

      switch (cmd) {
      case THREAD_NOTIFY_FLUSH:
            /*
             * flush_thread() zeroes thread->fpstate, so no need
             * to do anything here.
             *
             * FALLTHROUGH: Ensure we don't try to overwrite our newly
             * initialised state information on the first fault.
             */

      case THREAD_NOTIFY_RELEASE:
            iwmmxt_task_release(thread);
            break;

      case THREAD_NOTIFY_SWITCH:
            iwmmxt_task_switch(thread);
            break;
      }

      return NOTIFY_DONE;
}

static struct notifier_block iwmmxt_notifier_block = {
      .notifier_call    = iwmmxt_do,
};
#endif


static u32 __init xscale_cp_access_read(void)
{
      u32 value;

      __asm__ __volatile__ (
            "mrc  p15, 0, %0, c15, c1, 0\n\t"
            : "=r" (value));

      return value;
}

static void __init xscale_cp_access_write(u32 value)
{
      u32 temp;

      __asm__ __volatile__ (
            "mcr  p15, 0, %1, c15, c1, 0\n\t"
            "mrc  p15, 0, %0, c15, c1, 0\n\t"
            "mov  %0, %0\n\t"
            "sub  pc, pc, #4\n\t"
            : "=r" (temp) : "r" (value));
}

/*
 * Detect whether we have a MAC coprocessor (40 bit register) or an
 * iWMMXt coprocessor (64 bit registers) by loading 00000100:00000000
 * into a coprocessor register and reading it back, and checking
 * whether the upper word survived intact.
 */
static int __init cpu_has_iwmmxt(void)
{
      u32 lo;
      u32 hi;

      /*
       * This sequence is interpreted by the DSP coprocessor as:
       *    mar   acc0, %2, %3
       *    mra   %0, %1, acc0
       *
       * And by the iWMMXt coprocessor as:
       *    tmcrr wR0, %2, %3
       *    tmrrc %0, %1, wR0
       */
      __asm__ __volatile__ (
            "mcrr p0, 0, %2, %3, c0\n"
            "mrrc p0, 0, %0, %1, c0\n"
            : "=r" (lo), "=r" (hi)
            : "r" (0), "r" (0x100));

      return !!hi;
}


/*
 * If we detect that the CPU has iWMMXt (and CONFIG_IWMMXT=y), we
 * disable CP0/CP1 on boot, and let call_fpe() and the iWMMXt lazy
 * switch code handle iWMMXt context switching.  If on the other
 * hand the CPU has a DSP coprocessor, we keep access to CP0 enabled
 * all the time, and save/restore acc0 on context switch in non-lazy
 * fashion.
 */
static int __init xscale_cp0_init(void)
{
      u32 cp_access;

      cp_access = xscale_cp_access_read() & ~3;
      xscale_cp_access_write(cp_access | 1);

      if (cpu_has_iwmmxt()) {
#ifndef CONFIG_IWMMXT
            printk(KERN_WARNING "CAUTION: XScale iWMMXt coprocessor "
                  "detected, but kernel support is missing.\n");
#else
            printk(KERN_INFO "XScale iWMMXt coprocessor detected.\n");
            elf_hwcap |= HWCAP_IWMMXT;
            thread_register_notifier(&iwmmxt_notifier_block);
#endif
      } else {
            printk(KERN_INFO "XScale DSP coprocessor detected.\n");
            thread_register_notifier(&dsp_notifier_block);
            cp_access |= 1;
      }

      xscale_cp_access_write(cp_access);

      return 0;
}

late_initcall(xscale_cp0_init);

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