util/lxbios/cmos_lowlevel.c

/*****************************************************************************\
 * cmos_lowlevel.c
 * $Id: cmos_lowlevel.c,v 1.3 2006/01/24 00:25:39 dsp_llnl Exp $
 *****************************************************************************
 *  Copyright (C) 2002-2005 The Regents of the University of California.
 *  Produced at the Lawrence Livermore National Laboratory.
 *  Written by David S. Peterson <dsp@llnl.gov> <dave_peterson@pobox.com>.
 *  UCRL-CODE-2003-012
 *  All rights reserved.
 *
 *  This file is part of lxbios, a utility for reading/writing LinuxBIOS
 *  parameters and displaying information from the LinuxBIOS table.
 *  For details, see <http://www.llnl.gov/linux/lxbios/>.
 *
 *  Please also read the file DISCLAIMER which is included in this software
 *  distribution.
 *
 *  This program is free software; you can redistribute it and/or modify it
 *  under the terms of the GNU General Public License (as published by the
 *  Free Software Foundation) version 2, dated June 1991.
 *
 *  This program is distributed in the hope that it will be useful, but
 *  WITHOUT ANY WARRANTY; without even the IMPLIED WARRANTY OF
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the terms and
 *  conditions of the GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License along
 *  with this program; if not, write to the Free Software Foundation, Inc.,
 *  59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
\*****************************************************************************/

#include <sys/io.h>
#include "common.h"
#include "cmos_lowlevel.h"

typedef struct
 { unsigned byte_index;
   unsigned bit_offset;
 }
cmos_bit_op_location_t;

static unsigned cmos_bit_op_strategy (unsigned bit, unsigned bits_left,
                                      cmos_bit_op_location_t *where);
static unsigned char cmos_read_bits (const cmos_bit_op_location_t *where,
                                     unsigned nr_bits);
static void cmos_write_bits (const cmos_bit_op_location_t *where,
                             unsigned nr_bits, unsigned char value);
static unsigned char get_bits (unsigned long long value, unsigned bit,
                               unsigned nr_bits);
static void put_bits (unsigned char value, unsigned bit, unsigned nr_bits,
                      unsigned long long *result);

/****************************************************************************
 * get_bits
 *
 * Extract a value 'nr_bits' bits wide starting at bit position 'bit' from
 * 'value' and return the result.  It is assumed that 'nr_bits' is at most 8.
 ****************************************************************************/
static inline unsigned char get_bits (unsigned long long value, unsigned bit,
                                      unsigned nr_bits)
 { return (value >> bit) & ((unsigned char) ((1 << nr_bits) - 1)); }

/****************************************************************************
 * put_bits
 *
 * Extract the low order 'nr_bits' bits from 'value' and store them in the
 * value pointed to by 'result' starting at bit position 'bit'.  The bit
 * positions in 'result' where the result is stored are assumed to be
 * initially zero.
 ****************************************************************************/
static inline void put_bits (unsigned char value, unsigned bit,
                             unsigned nr_bits, unsigned long long *result)
 { *result += (value & ((unsigned char) ((1 << nr_bits) - 1))) << bit; }

/****************************************************************************
 * cmos_read
 *
 * Read value from nonvolatile RAM at position given by 'bit' and 'length'
 * and return this value.  The I/O privilege level of the currently executing
 * process must be set appropriately.
 ****************************************************************************/
unsigned long long cmos_read (unsigned bit, unsigned length)
 { cmos_bit_op_location_t where;
   unsigned next_bit, bits_left, nr_bits;
   unsigned long long result;
   unsigned char value;

   assert(!verify_cmos_op(bit, length));
   result = 0;

   for (next_bit = 0, bits_left = length;
        bits_left;
        next_bit += nr_bits, bits_left -= nr_bits)
    { nr_bits = cmos_bit_op_strategy(bit + next_bit, bits_left, &where);
      value = cmos_read_bits(&where, nr_bits);
      put_bits(value, next_bit, nr_bits, &result);
    }

   return result;
 }

/****************************************************************************
 * cmos_write
 *
 * Write 'data' to nonvolatile RAM at position given by 'bit' and 'length'.
 * The I/O privilege level of the currently executing process must be set
 * appropriately.
 ****************************************************************************/
void cmos_write (unsigned bit, unsigned length, unsigned long long value)
 { cmos_bit_op_location_t where;
   unsigned next_bit, bits_left, nr_bits;

   assert(!verify_cmos_op(bit, length));

   for (next_bit = 0, bits_left = length;
        bits_left;
        next_bit += nr_bits, bits_left -= nr_bits)
    { nr_bits = cmos_bit_op_strategy(bit + next_bit, bits_left, &where);
      cmos_write_bits(&where, nr_bits, get_bits(value, next_bit, nr_bits));
    }
 }

/****************************************************************************
 * cmos_read_byte
 *
 * Read a byte from nonvolatile RAM at a position given by 'index' and return
 * the result.  An 'index' value of 0 represents the first byte of
 * nonvolatile RAM.
 *
 * Note: the first 14 bytes of nonvolatile RAM provide an interface to the
 *       real time clock.
 ****************************************************************************/
unsigned char cmos_read_byte (unsigned index)
 { unsigned short port_0, port_1;

   assert(!verify_cmos_byte_index(index));

   if (index < 128)
    { port_0 = 0x70;
      port_1 = 0x71;
    }
   else
    { port_0 = 0x72;
      port_1 = 0x73;
    }

   outb(index, port_0);
   return inb(port_1);
 }

/****************************************************************************
 * cmos_write_byte
 *
 * Write 'value' to nonvolatile RAM at a position given by 'index'.  An
 * 'index' of 0 represents the first byte of nonvolatile RAM.
 *
 * Note: the first 14 bytes of nonvolatile RAM provide an interface to the
 *       real time clock.  Writing to any of these bytes will therefore
 *       affect its functioning.
 ****************************************************************************/
void cmos_write_byte (unsigned index, unsigned char value)
 { unsigned short port_0, port_1;

   assert(!verify_cmos_byte_index(index));

   if (index < 128)
    { port_0 = 0x70;
      port_1 = 0x71;
    }
   else
    { port_0 = 0x72;
      port_1 = 0x73;
    }

   outb(index, port_0);
   outb(value, port_1);
 }

/****************************************************************************
 * cmos_read_all
 *
 * Read all contents of CMOS memory into array 'data'.  The first 14 bytes of
 * 'data' are set to zero since this corresponds to the real time clock area.
 ****************************************************************************/
void cmos_read_all (unsigned char data[])
 { unsigned i;

   for (i = 0; i < CMOS_RTC_AREA_SIZE; i++)
      data[i] = 0;

   for (; i < CMOS_SIZE; i++)
      data[i] = cmos_read_byte(i);
 }

/****************************************************************************
 * cmos_write_all
 *
 * Update all of CMOS memory with the contents of array 'data'.  The first 14
 * bytes of 'data' are ignored since this corresponds to the real time clock
 * area.
 ****************************************************************************/
void cmos_write_all (unsigned char data[])
 { unsigned i;

   for (i = CMOS_RTC_AREA_SIZE; i < CMOS_SIZE; i++)
      cmos_write_byte(i, data[i]);
 }

/****************************************************************************
 * set_iopl
 *
 * Set the I/O privilege level of the executing process.  Root privileges are
 * required for performing this action.  A sufficient I/O privilege level
 * allows the process to access x86 I/O address space and to disable/reenable
 * interrupts while executing in user space.  Messing with the I/O privilege
 * level is therefore somewhat dangerous.
 ****************************************************************************/
void set_iopl (int level)
 { assert((level >= 0) && (level <= 3));

   if (iopl(level))
    { fprintf(stderr,
              "%s: iopl() system call failed.  You must be root to do "
              "this.\n",
              prog_name);
      exit(1);
    }
 }

/****************************************************************************
 * verify_cmos_op
 *
 * 'bit' represents a bit position in the nonvolatile RAM.  The first bit
 * (i.e. the lowest order bit of the first byte) of nonvolatile RAM is
 * labeled as bit 0.  'length' represents the width in bits of a value we
 * wish to read or write.  Perform sanity checking on 'bit' and 'length'.  If
 * no problems were encountered, return OK.  Else return an error code.
 ****************************************************************************/
int verify_cmos_op (unsigned bit, unsigned length)
 { if ((bit >= (8 * CMOS_SIZE)) || ((bit + length) > (8 * CMOS_SIZE)))
      return CMOS_AREA_OUT_OF_RANGE;

   if (bit < (8 * CMOS_RTC_AREA_SIZE))
      return CMOS_AREA_OVERLAPS_RTC;

   if (length > (8 * sizeof(unsigned long long)))
      return CMOS_AREA_TOO_WIDE;

   return OK;
 }

/****************************************************************************
 * cmos_bit_op_strategy
 *
 * Helper function used by cmos_read() and cmos_write() to determine which
 * bits to read or write next.
 ****************************************************************************/
static unsigned cmos_bit_op_strategy (unsigned bit, unsigned bits_left,
                                      cmos_bit_op_location_t *where)
 { unsigned max_bits;

   where->byte_index = bit >> 3;
   where->bit_offset = bit & 0x07;
   max_bits = 8 - where->bit_offset;
   return (bits_left > max_bits) ? max_bits : bits_left;
 }

/****************************************************************************
 * cmos_read_bits
 *
 * Read a chunk of bits from a byte location within CMOS memory.  Return the
 * value represented by the chunk of bits.
 ****************************************************************************/
static unsigned char cmos_read_bits (const cmos_bit_op_location_t *where,
                                     unsigned nr_bits)
 { return (cmos_read_byte(where->byte_index) >> where->bit_offset) &
          ((unsigned char) ((1 << nr_bits) - 1));
 }

/****************************************************************************
 * cmos_write_bits
 *
 * Write a chunk of bits (the low order 'nr_bits' bits of 'value') to an area
 * within a particular byte of CMOS memory.
 ****************************************************************************/
static void cmos_write_bits (const cmos_bit_op_location_t *where,
                             unsigned nr_bits, unsigned char value)
 { unsigned char n, mask;

   if (nr_bits == 8)
    { cmos_write_byte(where->byte_index, value);
      return;
    }

   n = cmos_read_byte(where->byte_index);
   mask = ((unsigned char) ((1 << nr_bits) - 1)) << where->bit_offset;
   n = (n & ~mask) + ((value << where->bit_offset) & mask);
   cmos_write_byte(where->byte_index, n);
 }