x86/PCI: allocate space from the end of a region, not the beginning

Allocate from the end of a region, not the beginning.

For example, if we need to allocate 0x800 bytes for a device on bus
0000:00 given these resources:

    [mem 0xbff00000-0xdfffffff] PCI Bus 0000:00
      [mem 0xc0000000-0xdfffffff] PCI Bus 0000:02

the available space at [mem 0xbff00000-0xbfffffff] is passed to the
alignment callback (pcibios_align_resource()).  Prior to this patch, we
would put the new 0x800 byte resource at the beginning of that available
space, i.e., at [mem 0xbff00000-0xbff007ff].

With this patch, we put it at the end, at [mem 0xbffff800-0xbfffffff].

Reference: https://bugzilla.kernel.org/show_bug.cgi?id=16228#c41
Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

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;
 }