- /* Tell the PCI layer not to allocate too close to the RAM area.. */
- low_mem_size = ((max_low_pfn << PAGE_SHIFT) + 0xfffff) & ~0xfffff;
- if (low_mem_size > pci_mem_start)
- pci_mem_start = low_mem_size;
+ /*
+ * Search for the bigest gap in the low 32 bits of the e820
+ * memory space.
+ */
+ 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;
+ }
+ }
+ if (start < last)
+ last = start;
+ }
+
+ /*
+ * 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("Allocating PCI resources starting at %08lx (gap: %08lx:%08lx)\n",
+ pci_mem_start, gapstart, gapsize);