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 * arch/i386/mm/boot_ioremap.c
 * Re-map functions for early boot-time before paging_init() when the 
 * boot-time pagetables are still in use
 * Written by Dave Hansen <haveblue@us.ibm.com>

 * We need to use the 2-level pagetable functions, but CONFIG_X86_PAE
 * keeps that from happening.  If anyone has a better way, I'm listening.
 * boot_pte_t is defined only if this all works correctly

#undef CONFIG_X86_PAE
#include <asm/page.h>
#include <asm/pgtable.h>
#include <asm/tlbflush.h>
#include <linux/init.h>
#include <linux/stddef.h>

 * I'm cheating here.  It is known that the two boot PTE pages are 
 * allocated next to each other.  I'm pretending that they're just
 * one big array. 


static unsigned long boot_pte_index(unsigned long vaddr) 
      return __pa(vaddr) >> PAGE_SHIFT;

static inline boot_pte_t* boot_vaddr_to_pte(void *address)
      boot_pte_t* boot_pg = (boot_pte_t*)pg0;
      return &boot_pg[boot_pte_index((unsigned long)address)];

 * This is only for a caller who is clever enough to page-align
 * phys_addr and virtual_source, and who also has a preference
 * about which virtual address from which to steal ptes
static void __boot_ioremap(unsigned long phys_addr, unsigned long nrpages, 
                void* virtual_source)
      boot_pte_t* pte;
      int i;
      char *vaddr = virtual_source;

      pte = boot_vaddr_to_pte(virtual_source);
      for (i=0; i < nrpages; i++, phys_addr += PAGE_SIZE, pte++) {
            set_pte(pte, pfn_pte(phys_addr>>PAGE_SHIFT, PAGE_KERNEL));

/* the virtual space we're going to remap comes from this array */
static __initdata char boot_ioremap_space[BOOT_IOREMAP_SIZE]
                   __attribute__ ((aligned (PAGE_SIZE)));

 * This only applies to things which need to ioremap before paging_init()
 * bt_ioremap() and plain ioremap() are both useless at this point.
 * When used, we're still using the boot-time pagetables, which only
 * have 2 PTE pages mapping the first 8MB
 * There is no unmap.  The boot-time PTE pages aren't used after boot.
 * If you really want the space back, just remap it yourself.
 * boot_ioremap(&ioremap_space-PAGE_OFFSET, BOOT_IOREMAP_SIZE)
__init void* boot_ioremap(unsigned long phys_addr, unsigned long size)
      unsigned long last_addr, offset;
      unsigned int nrpages;
      last_addr = phys_addr + size - 1;

      /* page align the requested address */
      offset = phys_addr & ~PAGE_MASK;
      phys_addr &= PAGE_MASK;
      size = PAGE_ALIGN(last_addr) - phys_addr;
      nrpages = size >> PAGE_SHIFT;
      if (nrpages > BOOT_IOREMAP_PAGES)
            return NULL;
      __boot_ioremap(phys_addr, nrpages, boot_ioremap_space);

      return &boot_ioremap_space[offset];

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