x86: cleanup e820_setup_gap(), add e820_search_gap(), v2

This is a preparatory patch for the next patch in series.
Moves some code from e820_setup_gap to a new function e820_search_gap.
This patch is a part of a bug fix where we walk the ACPI table to calculate
a gap for PCI optional devices.

v1->v2: Patch on top of tip/master.
	Fixes a bug introduced in the last patch about the typeof "last".
	Also the new function e820_search_gap now returns if we found a gap in
	e820_map.

Signed-off-by: Alok N Kataria <akataria@vmware.com>
Cc: lenb@kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 28 insertions, 15 deletions

diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index 3900ff51bc68..22cfd665224c 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -488,26 +488,22 @@ void __init update_e820(void)
 }
 
 /*
- * 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.
+ * Search for a gap in the e820 memory space from start_addr to 2^32.
  */
-__init void e820_setup_gap(void)
+__init int e820_search_gap(unsigned long *gapstart, unsigned long *gapsize,
+                unsigned long start_addr)
 {
-        unsigned long gapstart, gapsize, round;
-        unsigned long long last;
-        int i;
+        unsigned long long last = 0x100000000ull;
+        int i = e820.nr_map;
         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;
 
+                if (end < start_addr)
+                        continue;
+
                 /*
                  * Since "last" is at most 4GB, we know we'll
                  * fit in 32 bits if this condition is true
@@ -515,15 +511,32 @@ __init void e820_setup_gap(void)
                 if (last > end) {
                         unsigned long gap = last - end;
 
-                        if (gap > gapsize) {
-                                gapsize = gap;
-                                gapstart = end;
+                        if (gap >= *gapsize) {
+                                *gapsize = gap;
+                                *gapstart = end;
                                 found = 1;
                         }
                 }
                 if (start < last)
                         last = start;
         }
+        return found;
+}
+
+/*
+ * 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, round;
+        int found;
+
+        gapstart = 0x10000000;
+        gapsize = 0x400000;
+        found  = e820_search_gap(&gapstart, &gapsize, 0);
 
 #ifdef CONFIG_X86_64
         if (!found) {