pci: Automatically patch PCI vendor id and device id in PCI ROM

PCI devices with different vendor or device ids sometimes share
the same rom code. Only the ids and the checksum
differs in a boot rom for such devices.

The i825xx ethernet controller family is a typical example
which is implemented in hw/eepro100.c. It uses at least
3 different device ids, so normally 3 boot roms would be needed.

By automatically patching vendor id and device id (and the checksum)
in qemu, all emulated family members can share the same boot rom.

VGA bios roms are another example with different vendor and device ids.

Only qemu's built-in default rom files will be patched.

v2:
    * Patch also the vendor id (and remove the sanity check for vendor id).

v3:
    * Don't patch a rom file when its name was set by the user.
      Thus we avoid modifications of unknown rom data.

Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Stefan Weil <weil@mail.berlios.de>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/pci.c

@@ -61,7 +61,7 @@ struct BusInfo pci_bus_info = {
 
 static void pci_update_mappings(PCIDevice *d);
 static void pci_set_irq(void *opaque, int irq_num, int level);
-static int pci_add_option_rom(PCIDevice *pdev);
+static int pci_add_option_rom(PCIDevice *pdev, bool is_default_rom);
 static void pci_del_option_rom(PCIDevice *pdev);
 
 static uint16_t pci_default_sub_vendor_id = PCI_SUBVENDOR_ID_REDHAT_QUMRANET;
@@ -1571,6 +1571,7 @@ static int pci_qdev_init(DeviceState *qdev, DeviceInfo *base)
     PCIDeviceInfo *info = container_of(base, PCIDeviceInfo, qdev);
     PCIBus *bus;
     int devfn, rc;
+    bool is_default_rom;
 
     /* initialize cap_present for pci_is_express() and pci_config_size() */
     if (info->is_express) {
@@ -1591,9 +1592,12 @@ static int pci_qdev_init(DeviceState *qdev, DeviceInfo *base)
     }
 
     /* rom loading */
-    if (pci_dev->romfile == NULL && info->romfile != NULL)
+    is_default_rom = false;
+    if (pci_dev->romfile == NULL && info->romfile != NULL) {
         pci_dev->romfile = qemu_strdup(info->romfile);
-    pci_add_option_rom(pci_dev);
+        is_default_rom = true;
+    }
+    pci_add_option_rom(pci_dev, is_default_rom);
 
     if (bus->hotplug) {
         /* Let buses differentiate between hotplug and when device is
@@ -1701,8 +1705,64 @@ static void pci_map_option_rom(PCIDevice *pdev, int region_num, pcibus_t addr, p
     cpu_register_physical_memory(addr, size, pdev->rom_offset);
 }
 
+/* Patch the PCI vendor and device ids in a PCI rom image if necessary.
+   This is needed for an option rom which is used for more than one device. */
+static void pci_patch_ids(PCIDevice *pdev, uint8_t *ptr, int size)
+{
+    uint16_t vendor_id;
+    uint16_t device_id;
+    uint16_t rom_vendor_id;
+    uint16_t rom_device_id;
+    uint16_t rom_magic;
+    uint16_t pcir_offset;
+    uint8_t checksum;
+
+    /* Words in rom data are little endian (like in PCI configuration),
+       so they can be read / written with pci_get_word / pci_set_word. */
+
+    /* Only a valid rom will be patched. */
+    rom_magic = pci_get_word(ptr);
+    if (rom_magic != 0xaa55) {
+        PCI_DPRINTF("Bad ROM magic %04x\n", rom_magic);
+        return;
+    }
+    pcir_offset = pci_get_word(ptr + 0x18);
+    if (pcir_offset + 8 >= size || memcmp(ptr + pcir_offset, "PCIR", 4)) {
+        PCI_DPRINTF("Bad PCIR offset 0x%x or signature\n", pcir_offset);
+        return;
+    }
+
+    vendor_id = pci_get_word(pdev->config + PCI_VENDOR_ID);
+    device_id = pci_get_word(pdev->config + PCI_DEVICE_ID);
+    rom_vendor_id = pci_get_word(ptr + pcir_offset + 4);
+    rom_device_id = pci_get_word(ptr + pcir_offset + 6);
+
+    PCI_DPRINTF("%s: ROM id %04x%04x / PCI id %04x%04x\n", pdev->romfile,
+                vendor_id, device_id, rom_vendor_id, rom_device_id);
+
+    checksum = ptr[6];
+
+    if (vendor_id != rom_vendor_id) {
+        /* Patch vendor id and checksum (at offset 6 for etherboot roms). */
+        checksum += (uint8_t)rom_vendor_id + (uint8_t)(rom_vendor_id >> 8);
+        checksum -= (uint8_t)vendor_id + (uint8_t)(vendor_id >> 8);
+        PCI_DPRINTF("ROM checksum %02x / %02x\n", ptr[6], checksum);
+        ptr[6] = checksum;
+        pci_set_word(ptr + pcir_offset + 4, vendor_id);
+    }
+
+    if (device_id != rom_device_id) {
+        /* Patch device id and checksum (at offset 6 for etherboot roms). */
+        checksum += (uint8_t)rom_device_id + (uint8_t)(rom_device_id >> 8);
+        checksum -= (uint8_t)device_id + (uint8_t)(device_id >> 8);
+        PCI_DPRINTF("ROM checksum %02x / %02x\n", ptr[6], checksum);
+        ptr[6] = checksum;
+        pci_set_word(ptr + pcir_offset + 6, device_id);
+    }
+}
+
 /* Add an option rom for the device */
-static int pci_add_option_rom(PCIDevice *pdev)
+static int pci_add_option_rom(PCIDevice *pdev, bool is_default_rom)
 {
     int size;
     char *path;
@@ -1753,6 +1813,11 @@ static int pci_add_option_rom(PCIDevice *pdev)
     load_image(path, ptr);
     qemu_free(path);
 
+    if (is_default_rom) {
+        /* Only the default rom images will be patched (if needed). */
+        pci_patch_ids(pdev, ptr, size);
+    }
+
     pci_register_bar(pdev, PCI_ROM_SLOT, size,
                      0, pci_map_option_rom);