1 files changed, 59 insertions, 0 deletions

diff --git a/arch/x86_64/kernel/e820.c b/arch/x86_64/kernel/e820.c
index 657003e461e6..56516ac92e5d 100644
--- a/arch/x86_64/kernel/e820.c
+++ b/arch/x86_64/kernel/e820.c
@@ -511,3 +511,62 @@ void __init parse_memopt(char *p, char **from)
         end_user_pfn >>= PAGE_SHIFT;    
 } 
 
+unsigned long pci_mem_start = 0xaeedbabe;
+
+/*
+ * Search for the biggest gap in the low 32 bits of the e820
+ * memory space.  We pass this space to PCI to assign MMIO resources
+ * for hotplug or unconfigured devices in.
+ * Hopefully the BIOS let enough space left.
+ */
+__init void e820_setup_gap(void)
+{
+        unsigned long gapstart, gapsize;
+        unsigned long last;
+        int i;
+        int found = 0;
+
+        last = 0x100000000ull;
+        gapstart = 0x10000000;
+        gapsize = 0x400000;
+        i = e820.nr_map;
+        while (--i >= 0) {
+                unsigned long long start = e820.map[i].addr;
+                unsigned long long end = start + e820.map[i].size;
+
+                /*
+                 * Since "last" is at most 4GB, we know we'll
+                 * fit in 32 bits if this condition is true
+                 */
+                if (last > end) {
+                        unsigned long gap = last - end;
+
+                        if (gap > gapsize) {
+                                gapsize = gap;
+                                gapstart = end;
+                                found = 1;
+                        }
+                }
+                if (start < last)
+                        last = start;
+        }
+
+        if (!found) {
+                gapstart = (end_pfn << PAGE_SHIFT) + 1024*1024;
+                printk(KERN_ERR "PCI: Warning: Cannot find a gap in the 32bit address range\n"
+                       KERN_ERR "PCI: Unassigned devices with 32bit resource registers may break!\n");
+        }
+
+        /*
+         * Start allocating dynamic PCI memory a bit into the gap,
+         * aligned up to the nearest megabyte.
+         *
+         * Question: should we try to pad it up a bit (do something
+         * like " + (gapsize >> 3)" in there too?). We now have the
+         * technology.
+         */
+        pci_mem_start = (gapstart + 0xfffff) & ~0xfffff;
+
+        printk(KERN_INFO "Allocating PCI resources starting at %lx (gap: %lx:%lx)\n",
+                pci_mem_start, gapstart, gapsize);
+}