nvram.c

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/*
 * CMOS/NV-RAM driver for Linux
 *
 * Copyright (C) 1997 Roman Hodek <[e-mail]>
 * idea by and with help from Richard Jelinek <[e-mail]>
 * Portions copyright (c) 2001,2002 Sun Microsystems ([e-mail])
 *
 * This driver allows you to access the contents of the non-volatile memory in
 * the mc146818rtc.h real-time clock. This chip is built into all PCs and into
 * many Atari machines. In the former it's called "CMOS-RAM", in the latter
 * "NVRAM" (NV stands for non-volatile).
 *
 * The data are supplied as a (seekable) character device, /dev/nvram. The
 * size of this file is dependent on the controller.  The usual size is 114,
 * the number of freely available bytes in the memory (i.e., not used by the
 * RTC itself).
 *
 * Checksums over the NVRAM contents are managed by this driver. In case of a
 * bad checksum, reads and writes return -EIO. The checksum can be initialized
 * to a sane state either by ioctl(NVRAM_INIT) (clear whole NVRAM) or
 * ioctl(NVRAM_SETCKS) (doesn't change contents, just makes checksum valid
 * again; use with care!)
 *
 * This file also provides some functions for other parts of the kernel that
 * want to access the NVRAM: nvram_{read,write,check_checksum,set_checksum}.
 * Obviously this can be used only if this driver is always configured into
 * the kernel and is not a module. Since the functions are used by some Atari
 * drivers, this is the case on the Atari.
 *
 *
 * 	1.1	Cesar Barros: SMP locking fixes
 * 		added changelog
 * 	1.2	Erik Gilling: Cobalt Networks support
 * 		Tim Hockin: general cleanup, Cobalt support
 */

#define NVRAM_VERSION	"1.2"

#include <linux/module.h>
#include <linux/smp_lock.h>
#include <linux/nvram.h>

#define PC		1
#define ATARI		2

/* select machine configuration */
#if defined(CONFIG_ATARI)
#  define MACH ATARI
#elif defined(__i386__) || defined(__x86_64__) || defined(__arm__)  /* and others?? */
#  define MACH PC
#else
#  error Cannot build nvram driver for this machine configuration.
#endif

#if MACH == PC

/* RTC in a PC */
#define CHECK_DRIVER_INIT()	1

/* On PCs, the checksum is built only over bytes 2..31 */
#define PC_CKS_RANGE_START	2
#define PC_CKS_RANGE_END	31
#define PC_CKS_LOC		32
#define NVRAM_BYTES		(128-NVRAM_FIRST_BYTE)

#define mach_check_checksum	pc_check_checksum
#define mach_set_checksum	pc_set_checksum
#define mach_proc_infos		pc_proc_infos

#endif

#if MACH == ATARI

/* Special parameters for RTC in Atari machines */
#include <asm/atarihw.h>
#include <asm/atariints.h>
#define RTC_PORT(x)		(TT_RTC_BAS + 2*(x))
#define CHECK_DRIVER_INIT()	(MACH_IS_ATARI && ATARIHW_PRESENT(TT_CLK))

#define NVRAM_BYTES		50

/* On Ataris, the checksum is over all bytes except the checksum bytes
 * themselves; these are at the very end */
#define ATARI_CKS_RANGE_START	0
#define ATARI_CKS_RANGE_END	47
#define ATARI_CKS_LOC		48

#define mach_check_checksum	atari_check_checksum
#define mach_set_checksum	atari_set_checksum
#define mach_proc_infos		atari_proc_infos

#endif

/* Note that *all* calls to CMOS_READ and CMOS_WRITE must be done with
 * rtc_lock held. Due to the index-port/data-port design of the RTC, we
 * don't want two different things trying to get to it at once. (e.g. the
 * periodic 11 min sync from time.c vs. this driver.)
 */

#include <linux/types.h>
#include <linux/errno.h>
#include <linux/miscdevice.h>
#include <linux/slab.h>
#include <linux/ioport.h>
#include <linux/fcntl.h>
#include <linux/mc146818rtc.h>
#include <linux/init.h>
#include <linux/proc_fs.h>
#include <linux/spinlock.h>

#include <asm/io.h>
#include <asm/uaccess.h>
#include <asm/system.h>

static DEFINE_SPINLOCK(nvram_state_lock);
static int nvram_open_cnt;	/* #times opened */
static int nvram_open_mode;	/* special open modes */
#define NVRAM_WRITE		1 /* opened for writing (exclusive) */
#define NVRAM_EXCL		2 /* opened with O_EXCL */

static int mach_check_checksum(void);
static void mach_set_checksum(void);

#ifdef CONFIG_PROC_FS
static int mach_proc_infos(unsigned char *contents, char *buffer, int *len,
    off_t *begin, off_t offset, int size);
#endif

/*
 * These functions are provided to be called internally or by other parts of
 * the kernel. It's up to the caller to ensure correct checksum before reading
 * or after writing (needs to be done only once).
 *
 * It is worth noting that these functions all access bytes of general
 * purpose memory in the NVRAM - that is to say, they all add the
 * NVRAM_FIRST_BYTE offset.  Pass them offsets into NVRAM as if you did not 
 * know about the RTC cruft.
 */

unsigned char
__nvram_read_byte(int i)
{
	return CMOS_READ(NVRAM_FIRST_BYTE + i);
}

unsigned char
nvram_read_byte(int i)
{
	unsigned long flags;
	unsigned char c;

	spin_lock_irqsave(&rtc_lock, flags);
	c = __nvram_read_byte(i);
	spin_unlock_irqrestore(&rtc_lock, flags);
	return c;
}

/* This races nicely with trying to read with checksum checking (nvram_read) */
void
__nvram_write_byte(unsigned char c, int i)
{
	CMOS_WRITE(c, NVRAM_FIRST_BYTE + i);
}

void
nvram_write_byte(unsigned char c, int i)
{
	unsigned long flags;

	spin_lock_irqsave(&rtc_lock, flags);
	__nvram_write_byte(c, i);
	spin_unlock_irqrestore(&rtc_lock, flags);
}

int
__nvram_check_checksum(void)
{
	return mach_check_checksum();
}

int
nvram_check_checksum(void)
{
	unsigned long flags;
	int rv;

	spin_lock_irqsave(&rtc_lock, flags);
	rv = __nvram_check_checksum();
	spin_unlock_irqrestore(&rtc_lock, flags);
	return rv;
}

static void
__nvram_set_checksum(void)
{
	mach_set_checksum();
}

#if 0
void
nvram_set_checksum(void)
{
	unsigned long flags;

	spin_lock_irqsave(&rtc_lock, flags);
	__nvram_set_checksum();
	spin_unlock_irqrestore(&rtc_lock, flags);
}
#endif  /*  0  */

/*
 * The are the file operation function for user access to /dev/nvram
 */

static loff_t nvram_llseek(struct file *file,loff_t offset, int origin )
{
	lock_kernel();
	switch (origin) {
	case 0:
		/* nothing to do */
		break;
	case 1:
		offset += file->f_pos;
		break;
	case 2:
		offset += NVRAM_BYTES;
		break;
	}
	unlock_kernel();
	return (offset >= 0) ? (file->f_pos = offset) : -EINVAL;
}

static ssize_t
nvram_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
{
	unsigned char contents[NVRAM_BYTES];
	unsigned i = *ppos;
	unsigned char *tmp;

	spin_lock_irq(&rtc_lock);

	if (!__nvram_check_checksum())
		goto checksum_err;

	for (tmp = contents; count-- > 0 && i < NVRAM_BYTES; ++i, ++tmp)
		*tmp = __nvram_read_byte(i);

	spin_unlock_irq(&rtc_lock);

	if (copy_to_user(buf, contents, tmp - contents))
		return -EFAULT;

	*ppos = i;

	return tmp - contents;

      checksum_err:
	spin_unlock_irq(&rtc_lock);
	return -EIO;
}

static ssize_t
nvram_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
{
	unsigned char contents[NVRAM_BYTES];
	unsigned i = *ppos;
	unsigned char *tmp;
	int len;

	len = (NVRAM_BYTES - i) < count ? (NVRAM_BYTES - i) : count;
	if (copy_from_user(contents, buf, len))
		return -EFAULT;

	spin_lock_irq(&rtc_lock);

	if (!__nvram_check_checksum())
		goto checksum_err;

	for (tmp = contents; count-- > 0 && i < NVRAM_BYTES; ++i, ++tmp)
		__nvram_write_byte(*tmp, i);

	__nvram_set_checksum();

	spin_unlock_irq(&rtc_lock);

	*ppos = i;

	return tmp - contents;

      checksum_err:
	spin_unlock_irq(&rtc_lock);
	return -EIO;
}

static int
nvram_ioctl(struct inode *inode, struct file *file,
    unsigned int cmd, unsigned long arg)
{
	int i;

	switch (cmd) {

	case NVRAM_INIT:
		/* initialize NVRAM contents and checksum */
		if (!capable(CAP_SYS_ADMIN))
			return -EACCES;

		spin_lock_irq(&rtc_lock);

		for (i = 0; i < NVRAM_BYTES; ++i)
			__nvram_write_byte(0, i);
		__nvram_set_checksum();

		spin_unlock_irq(&rtc_lock);
		return 0;

	case NVRAM_SETCKS:
		/* just set checksum, contents unchanged (maybe useful after 
		 * checksum garbaged somehow...) */
		if (!capable(CAP_SYS_ADMIN))
			return -EACCES;

		spin_lock_irq(&rtc_lock);
		__nvram_set_checksum();
		spin_unlock_irq(&rtc_lock);
		return 0;

	default:
		return -ENOTTY;
	}
}

static int
nvram_open(struct inode *inode, struct file *file)
{
	spin_lock(&nvram_state_lock);

	if ((nvram_open_cnt && (file->f_flags & O_EXCL)) ||
	    (nvram_open_mode & NVRAM_EXCL) ||
	    ((file->f_mode & 2) && (nvram_open_mode & NVRAM_WRITE))) {
		spin_unlock(&nvram_state_lock);
		return -EBUSY;
	}

	if (file->f_flags & O_EXCL)
		nvram_open_mode |= NVRAM_EXCL;
	if (file->f_mode & 2)
		nvram_open_mode |= NVRAM_WRITE;
	nvram_open_cnt++;

	spin_unlock(&nvram_state_lock);

	return 0;
}

static int
nvram_release(struct inode *inode, struct file *file)
{
	spin_lock(&nvram_state_lock);

	nvram_open_cnt--;

	/* if only one instance is open, clear the EXCL bit */
	if (nvram_open_mode & NVRAM_EXCL)
		nvram_open_mode &= ~NVRAM_EXCL;
	if (file->f_mode & 2)
		nvram_open_mode &= ~NVRAM_WRITE;