hw: better i440 emulation

updated version of an old patch
http://xenon.stanford.edu/~eswierk/misc/qemu-linuxbios/qemu-piix-ram-size.patch
that together with
http://www.mail-archive.com/linuxbios@linuxbios.org/msg02390.html
(which is already in coreboot trunk) allows coreboot to autodetect the amount of RAM within qemu/kvm from a register in i440 northbridge.

The message on the old patch states:
Unfortunately the current version of qemu does not set these
registers, but I have patched qemu so that it emulates the i440 more
faithfully in this regard.
Signed-off-by: NBernhard M. Wiedemann <qemudevbmw@lsmod.de>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

hw/pc.c

@@ -924,7 +924,7 @@ static void pc_init1(ram_addr_t ram_size,
     isa_irq = qemu_allocate_irqs(isa_irq_handler, isa_irq_state, 24);
 
     if (pci_enabled) {
-        pci_bus = i440fx_init(&i440fx_state, &piix3_devfn, isa_irq);
+        pci_bus = i440fx_init(&i440fx_state, &piix3_devfn, isa_irq, ram_size);
     } else {
         pci_bus = NULL;
         isa_bus_new(NULL);

hw/pc.h

@@ -107,7 +107,7 @@ int pcspk_audio_init(qemu_irq *pic);
 struct PCII440FXState;
 typedef struct PCII440FXState PCII440FXState;
 
-PCIBus *i440fx_init(PCII440FXState **pi440fx_state, int *piix_devfn, qemu_irq *pic);
+PCIBus *i440fx_init(PCII440FXState **pi440fx_state, int *piix_devfn, qemu_irq *pic, int ram_size);
 void i440fx_set_smm(PCII440FXState *d, int val);
 void i440fx_init_memory_mappings(PCII440FXState *d);
 

hw/piix_pci.c

@@ -213,7 +213,7 @@ static int i440fx_initfn(PCIDevice *dev)
     return 0;
 }
 
-PCIBus *i440fx_init(PCII440FXState **pi440fx_state, int *piix3_devfn, qemu_irq *pic)
+PCIBus *i440fx_init(PCII440FXState **pi440fx_state, int *piix3_devfn, qemu_irq *pic, int ram_size)
 {
     DeviceState *dev;
     PCIBus *b;
@@ -238,6 +238,11 @@ PCIBus *i440fx_init(PCII440FXState **pi440fx_state, int *piix3_devfn, qemu_irq *
 
     *piix3_devfn = piix3->dev.devfn;
 
+    ram_size = ram_size / 8 / 1024 / 1024;
+    if (ram_size > 255)
+        ram_size = 255;
+    (*pi440fx_state)->dev.config[0x57]=ram_size;
+
     return b;
 }