[Qemu-devel] [PATCH] [0.12] Map BIOS f-segment as RAM, not as ROM

[Alexander Graf <agraf@suse.de>]

SeaBIOS needs to write to the f-segment. So it needs to have some way to set
that from read-only to read-write, write in it and when it's done set it to
read-only again.

On PCI we have a mechanism for that. The ISA machine does not though. To stay
regression free and happily enable users to continue using the -M isapc machine
let's just map it as RAM on the ISA PC.

Signed-off-by: Alexander Graf <agraf@suse.de>
---
 hw/pc.c |   22 ++++++++++++++++++++--
 1 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/hw/pc.c b/hw/pc.c
index 8c1b7ea..90373cf 100644
--- a/hw/pc.c
+++ b/hw/pc.c
@@ -982,7 +982,7 @@ static void pc_init1(ram_addr_t ram_size,
     int ret, linux_boot, i;
     ram_addr_t ram_addr, bios_offset, option_rom_offset;
     ram_addr_t below_4g_mem_size, above_4g_mem_size = 0;
-    int bios_size, isa_bios_size;
+    int bios_size, isa_bios_size, f_seg_type;
     PCIBus *pci_bus;
     ISADevice *isa_dev;
     int piix3_devfn = -1;
@@ -1073,9 +1073,27 @@ static void pc_init1(ram_addr_t ram_size,
     isa_bios_size = bios_size;
     if (isa_bios_size > (128 * 1024))
         isa_bios_size = 128 * 1024;
+
+    /* XXX
+     *
+     * Usually we would map this region read only, have the BIOS set it r/w
+     * when it needs to and have the BIOS also set it r/o when it's done
+     * messing with it.
+     *
+     * Unfortunately we don't export any device to the ISA PC machine that
+     * could do the r/w <-> r/o transition, so let's just always map it r/w
+     * there for now.
+     */
+
+    if (pci_enabled) {
+        f_seg_type = IO_MEM_ROM;
+    } else {
+        f_seg_type = 0;
+    }
+
     cpu_register_physical_memory(0x100000 - isa_bios_size,
                                  isa_bios_size,
-                                 (bios_offset + bios_size - isa_bios_size) | IO_MEM_ROM);
+                                 (bios_offset + bios_size - isa_bios_size) | f_seg_type);
 
 
 
-- 
1.6.0.2