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fiq.c

/*
 *  linux/arch/arm/kernel/fiq.c
 *
 *  Copyright (C) 1998 Russell King
 *  Copyright (C) 1998, 1999 Phil Blundell
 *
 *  FIQ support written by Philip Blundell <philb@gnu.org>, 1998.
 *
 *  FIQ support re-written by Russell King to be more generic
 *
 * We now properly support a method by which the FIQ handlers can
 * be stacked onto the vector.  We still do not support sharing
 * the FIQ vector itself.
 *
 * Operation is as follows:
 *  1. Owner A claims FIQ:
 *     - default_fiq relinquishes control.
 *  2. Owner A:
 *     - inserts code.
 *     - sets any registers,
 *     - enables FIQ.
 *  3. Owner B claims FIQ:
 *     - if owner A has a relinquish function.
 *       - disable FIQs.
 *       - saves any registers.
 *       - returns zero.
 *  4. Owner B:
 *     - inserts code.
 *     - sets any registers,
 *     - enables FIQ.
 *  5. Owner B releases FIQ:
 *     - Owner A is asked to reacquire FIQ:
 *     - inserts code.
 *     - restores saved registers.
 *     - enables FIQ.
 *  6. Goto 3
 */
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/seq_file.h>

#include <asm/cacheflush.h>
#include <asm/fiq.h>
#include <asm/irq.h>
#include <asm/system.h>
#include <asm/uaccess.h>

static unsigned long no_fiq_insn;

/* Default reacquire function
 * - we always relinquish FIQ control
 * - we always reacquire FIQ control
 */
static int fiq_def_op(void *ref, int relinquish)
{
      if (!relinquish)
            set_fiq_handler(&no_fiq_insn, sizeof(no_fiq_insn));

      return 0;
}

static struct fiq_handler default_owner = {
      .name = "default",
      .fiq_op = fiq_def_op,
};

static struct fiq_handler *current_fiq = &default_owner;

int show_fiq_list(struct seq_file *p, void *v)
{
      if (current_fiq != &default_owner)
            seq_printf(p, "FIQ:              %s\n", current_fiq->name);

      return 0;
}

void set_fiq_handler(void *start, unsigned int length)
{
      memcpy((void *)0xffff001c, start, length);
      flush_icache_range(0xffff001c, 0xffff001c + length);
      if (!vectors_high())
            flush_icache_range(0x1c, 0x1c + length);
}

/*
 * Taking an interrupt in FIQ mode is death, so both these functions
 * disable irqs for the duration.  Note - these functions are almost
 * entirely coded in assembly.
 */
void __attribute__((naked)) set_fiq_regs(struct pt_regs *regs)
{
      register unsigned long tmp;
      asm volatile (
      "mov  ip, sp\n\
      stmfd sp!, {fp, ip, lr, pc}\n\
      sub   fp, ip, #4\n\
      mrs   %0, cpsr\n\
      msr   cpsr_c, %2  @ select FIQ mode\n\
      mov   r0, r0\n\
      ldmia %1, {r8 - r14}\n\
      msr   cpsr_c, %0  @ return to SVC mode\n\
      mov   r0, r0\n\
      ldmfd sp, {fp, sp, pc}"
      : "=&r" (tmp)
      : "r" (&regs->ARM_r8), "I" (PSR_I_BIT | PSR_F_BIT | FIQ_MODE));
}

void __attribute__((naked)) get_fiq_regs(struct pt_regs *regs)
{
      register unsigned long tmp;
      asm volatile (
      "mov  ip, sp\n\
      stmfd sp!, {fp, ip, lr, pc}\n\
      sub   fp, ip, #4\n\
      mrs   %0, cpsr\n\
      msr   cpsr_c, %2  @ select FIQ mode\n\
      mov   r0, r0\n\
      stmia %1, {r8 - r14}\n\
      msr   cpsr_c, %0  @ return to SVC mode\n\
      mov   r0, r0\n\
      ldmfd sp, {fp, sp, pc}"
      : "=&r" (tmp)
      : "r" (&regs->ARM_r8), "I" (PSR_I_BIT | PSR_F_BIT | FIQ_MODE));
}

int claim_fiq(struct fiq_handler *f)
{
      int ret = 0;

      if (current_fiq) {
            ret = -EBUSY;

            if (current_fiq->fiq_op != NULL)
                  ret = current_fiq->fiq_op(current_fiq->dev_id, 1);
      }

      if (!ret) {
            f->next = current_fiq;
            current_fiq = f;
      }

      return ret;
}

void release_fiq(struct fiq_handler *f)
{
      if (current_fiq != f) {
            printk(KERN_ERR "%s FIQ trying to release %s FIQ\n",
                   f->name, current_fiq->name);
            dump_stack();
            return;
      }

      do
            current_fiq = current_fiq->next;
      while (current_fiq->fiq_op(current_fiq->dev_id, 0));
}

void enable_fiq(int fiq)
{
      enable_irq(fiq + FIQ_START);
}

void disable_fiq(int fiq)
{
      disable_irq(fiq + FIQ_START);
}

EXPORT_SYMBOL(set_fiq_handler);
EXPORT_SYMBOL(set_fiq_regs);
EXPORT_SYMBOL(get_fiq_regs);
EXPORT_SYMBOL(claim_fiq);
EXPORT_SYMBOL(release_fiq);
EXPORT_SYMBOL(enable_fiq);
EXPORT_SYMBOL(disable_fiq);

void __init init_FIQ(void)
{
      no_fiq_insn = *(unsigned long *)0xffff001c;
}

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