ram.c

/*
 * Copyright (c) 2000, 2001, 2002, 2003, 2004, 2005, 2008, 2009
 *      The President and Fellows of Harvard College.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <types.h>
#include <lib.h>
#include <vm.h>
#include <mainbus.h>


vaddr_t firstfree;   /* first free virtual address; set by start.S */

static paddr_t firstpaddr;  /* address of first free physical page */
static paddr_t lastpaddr;   /* one past end of last free physical page */

/*
 * Called very early in system boot to figure out how much physical
 * RAM is available.
 */
void
ram_bootstrap(void)
{
        size_t ramsize;
        
        /* Get size of RAM. */
        ramsize = mainbus_ramsize();

        /*
         * This is the same as the last physical address, as long as
         * we have less than 508 megabytes of memory. If we had more,
         * various annoying properties of the MIPS architecture would
         * force the RAM to be discontiguous. This is not a case we 
         * are going to worry about.
         */
        if (ramsize > 508*1024*1024) {
                ramsize = 508*1024*1024;
        }

        lastpaddr = ramsize;

        /* 
         * Get first free virtual address from where start.S saved it.
         * Convert to physical address.
         */
        firstpaddr = firstfree - MIPS_KSEG0;

        kprintf("%uk physical memory available\n", 
                (lastpaddr-firstpaddr)/1024);
}

/*
 * This function is for allocating physical memory prior to VM
 * initialization.
 *
 * The pages it hands back will not be reported to the VM system when
 * the VM system calls ram_getsize(). If it's desired to free up these
 * pages later on after bootup is complete, some mechanism for adding
 * them to the VM system's page management must be implemented.
 * Alternatively, one can do enough VM initialization early so that
 * this function is never needed.
 *
 * Note: while the error return value of 0 is a legal physical address,
 * it's not a legal *allocatable* physical address, because it's the
 * page with the exception handlers on it.
 *
 * This function should not be called once the VM system is initialized, 
 * so it is not synchronized.
 */
paddr_t
ram_stealmem(unsigned long npages)
{
        size_t size;
        paddr_t paddr;

        size = npages * PAGE_SIZE;

        if (firstpaddr + size > lastpaddr) {
                return 0;
        }

        paddr = firstpaddr;
        firstpaddr += size;

        return paddr;
}

/*
 * This function is intended to be called by the VM system when it
 * initializes in order to find out what memory it has available to
 * manage.
 *
 * This function should not be called once the VM system is initialized, 
 * so it is not synchronized.
 */
void
ram_getsize(paddr_t *lo, paddr_t *hi)
{
        *lo = firstpaddr;
        *hi = lastpaddr;
        firstpaddr = lastpaddr = 0;
}