[PATCH] Early ioremap support for ia32

Patch from Patricia Gaughen <gone@us.ibm.com>,
		Dave Hansen <haveblue@us.ibm.com>

It provides a very early sort of kmap-by-hand.

The patch is used by the x440 discontigmem to map the srat tables into low
memory so that the memory can be setup.  This remap function is used very
early in the boot process...  at the start of setup_arch().

This functionality is only available to Summit and NUMAQ.  It will work on
other platforms, but they do not need it.

arch/i386/Kconfig

@@ -752,6 +752,13 @@ config HAVE_DEC_LOCK
 	depends on (SMP || PREEMPT) && X86_CMPXCHG
 	default y
 
+# turning this on wastes a bunch of space.
+# Summit needs it only when NUMA is on
+config BOOT_IOREMAP
+	bool
+	depends on (X86_SUMMIT && NUMA)
+	default y
+
 endmenu
 
 

arch/i386/mm/Makefile

@@ -7,3 +7,4 @@ obj-y	:= init.o pgtable.o fault.o ioremap.o extable.o pageattr.o
 obj-$(CONFIG_DISCONTIGMEM)	+= discontig.o
 obj-$(CONFIG_HUGETLB_PAGE) += hugetlbpage.o
 obj-$(CONFIG_HIGHMEM) += highmem.o
+obj-$(CONFIG_BOOT_IOREMAP) += boot_ioremap.o

arch/i386/mm/boot_ioremap.c

+/*
+ * 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 happenning.  If anyone has a better way, I'm listening.
+ *
+ * boot_pte_t is defined only if this all works correctly
+ */
+
+#include <linux/config.h>
+#undef CONFIG_X86_PAE
+#include <asm/page.h>
+#include <asm/pgtable.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. 
+ */
+
+#define BOOT_PTE_PTRS (PTRS_PER_PTE*2)
+#define boot_pte_index(address) \
+	     (((address) >> PAGE_SHIFT) & (BOOT_PTE_PTRS - 1))
+
+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;
+
+	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 */
+#define BOOT_IOREMAP_PAGES 4
+#define BOOT_IOREMAP_SIZE (BOOT_IOREMAP_PAGES*PAGE_SIZE)
+__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];
+}

include/asm-i386/page.h

@@ -49,6 +49,7 @@ typedef struct { unsigned long long pgd; } pgd_t;
 typedef struct { unsigned long pte_low; } pte_t;
 typedef struct { unsigned long pmd; } pmd_t;
 typedef struct { unsigned long pgd; } pgd_t;
+#define boot_pte_t pte_t /* or would you rather have a typedef */
 #define pte_val(x)	((x).pte_low)
 #define HPAGE_SHIFT	22
 #endif