LinuxQuestions.org - About use FIQ for SPI slave in device driver.

But linux seem can't used fiq, and fiq only used simple capability.

This is fig.c in linux,I don't know how do used this function?

/*
* 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/seq_file.h>

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

#if __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)
#warning This file requires GCC 3.3.x or older to build. Alternatively,
#warning please talk to GCC people to resolve the issues with the
#warning assembly clobber list.
#endif

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.
*/
void set_fiq_regs(struct pt_regs *regs)
{
register unsigned long tmp;
__asm__ volatile (
"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"
: "=&r" (tmp)
: "r" (&regs->ARM_r8), "I" (PSR_I_BIT | PSR_F_BIT | FIQ_MODE)
/* These registers aren't modified by the above code in a way
visible to the compiler, but we mark them as clobbers anyway
so that GCC won't put any of the input or output operands in
them. */
: "r8", "r9", "r10", "r11", "r12", "r13", "r14");
}

void get_fiq_regs(struct pt_regs *regs)
{
register unsigned long tmp;
__asm__ volatile (
"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"
: "=&r" (tmp)
: "r" (&regs->ARM_r8), "I" (PSR_I_BIT | PSR_F_BIT | FIQ_MODE)
/* These registers aren't modified by the above code in a way
visible to the compiler, but we mark them as clobbers anyway
so that GCC won't put any of the input or output operands in
them. */
: "r8", "r9", "r10", "r11", "r12", "r13", "r14");
}

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;
}