1 files changed, 11 insertions, 6 deletions

diff --git a/arch/x86/pci/i386.c b/arch/x86/pci/i386.c
index 55253095be84..826140af3c3c 100644
--- a/arch/x86/pci/i386.c
+++ b/arch/x86/pci/i386.c
@@ -65,16 +65,21 @@ pcibios_align_resource(void *data, const struct resource *res,
                         resource_size_t size, resource_size_t align)
 {
         struct pci_dev *dev = data;
-        resource_size_t start = res->start;
+        resource_size_t start = round_down(res->end - size + 1, align);
 
         if (res->flags & IORESOURCE_IO) {
-                if (skip_isa_ioresource_align(dev))
-                        return start;
-                if (start & 0x300)
-                        start = (start + 0x3ff) & ~0x3ff;
+
+                /*
+                 * If we're avoiding ISA aliases, the largest contiguous I/O
+                 * port space is 256 bytes.  Clearing bits 9 and 10 preserves
+                 * all 256-byte and smaller alignments, so the result will
+                 * still be correctly aligned.
+                 */
+                if (!skip_isa_ioresource_align(dev))
+                        start &= ~0x300;
         } else if (res->flags & IORESOURCE_MEM) {
                 if (start < BIOS_END)
-                        start = BIOS_END;
+                        start = res->end;       /* fail; no space */
         }
         return start;
 }