[SeaBIOS] [PATCH 3/6] Simplify pci_bios_init_root_regions().

[Kevin O'Connor]

Add some comments and refactor out some duplicated code.

Signed-off-by: Kevin O'Connor 
---
 src/pciinit.c |   38 +++++++++++++-------------------------
 1 files changed, 13 insertions(+), 25 deletions(-)

diff --git a/src/pciinit.c b/src/pciinit.c
index 62583a3..ccf71d1 100644
--- a/src/pciinit.c
+++ b/src/pciinit.c
@@ -439,38 +439,26 @@ static void pci_bios_check_device_in_bus(int bus)

#define ROOT_BASE(top, sum, max) ALIGN_DOWN((top)-(sum),(max) ?: 1)

+// Setup region bases (given the regions' size and alignment)
 static int pci_bios_init_root_regions(u32 start, u32 end)
 {
     struct pci_bus *bus = &busses[0];

bus->r[PCI_REGION_TYPE_IO].base = 0xc000;

-    if (bus->r[PCI_REGION_TYPE_MEM].sum < bus->r[PCI_REGION_TYPE_PREFMEM].sum) {
-        bus->r[PCI_REGION_TYPE_MEM].base =
-            ROOT_BASE(end,
-                      bus->r[PCI_REGION_TYPE_MEM].sum,
-                      bus->r[PCI_REGION_TYPE_MEM].max);
-        bus->r[PCI_REGION_TYPE_PREFMEM].base =
-            ROOT_BASE(bus->r[PCI_REGION_TYPE_MEM].base,
-                      bus->r[PCI_REGION_TYPE_PREFMEM].sum,
-                      bus->r[PCI_REGION_TYPE_PREFMEM].max);
-        if (bus->r[PCI_REGION_TYPE_PREFMEM].base >= start) {
-            return 0;
-        }
-    } else {
-        bus->r[PCI_REGION_TYPE_PREFMEM].base =
-            ROOT_BASE(end,
-                      bus->r[PCI_REGION_TYPE_PREFMEM].sum,
-                      bus->r[PCI_REGION_TYPE_PREFMEM].max);
-        bus->r[PCI_REGION_TYPE_MEM].base =
-            ROOT_BASE(bus->r[PCI_REGION_TYPE_PREFMEM].base,
-                      bus->r[PCI_REGION_TYPE_MEM].sum,
-                      bus->r[PCI_REGION_TYPE_MEM].max);
-        if (bus->r[PCI_REGION_TYPE_MEM].base >= start) {
-            return 0;
-        }
+    int reg1 = PCI_REGION_TYPE_PREFMEM, reg2 = PCI_REGION_TYPE_MEM;
+    if (bus->r[reg1].sum < bus->r[reg2].sum) {
+        // Swap regions so larger area is more likely to align well.
+        reg1 = PCI_REGION_TYPE_MEM;
+        reg2 = PCI_REGION_TYPE_PREFMEM;
     }
-    return -1;
+    bus->r[reg2].base = ROOT_BASE(end, bus->r[reg2].sum, bus->r[reg2].max);
+    bus->r[reg1].base = ROOT_BASE(bus->r[reg2].base, bus->r[reg1].sum
+                                  , bus->r[reg1].max);
+    if (bus->r[reg1].base < start)
+        // Memory range requested is larger than available.
+        return -1;
+    return 0;
 }