[Qemu-devel] [PATCH 5/6] vfio/pci: Fixup PCI option ROMs

[Alex Williamson <alex.williamson@redhat.com>]

Devices like Intel graphics are known to not only have bad checksums,
but also the wrong device ID.  This is not so surprising given that
the video BIOS is typically part of the system firmware image rather
that embedded into the device and needs to support any IGD device
installed into the system.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---
 hw/vfio/pci.c |   30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index 82c3771..ebbc9d6 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -832,6 +832,36 @@ static void vfio_pci_load_rom(VFIOPCIDevice *vdev)
             break;
         }
     }
+
+    /*
+     * Test the ROM signature against our device, if the vendor is correct
+     * but the device ID doesn't match, store the correct device ID and
+     * recompute the checksum.  Intel IGD devices need this and are known
+     * to have bogus checksums so we can't simply adjust the checksum.
+     */
+    if (pci_get_word(vdev->rom) == 0xaa55 &&
+        pci_get_word(vdev->rom + 0x18) + 8 < vdev->rom_size &&
+        !memcmp(vdev->rom + pci_get_word(vdev->rom + 0x18), "PCIR", 4)) {
+        uint16_t vid, did;
+
+        vid = pci_get_word(vdev->rom + pci_get_word(vdev->rom + 0x18) + 4);
+        did = pci_get_word(vdev->rom + pci_get_word(vdev->rom + 0x18) + 6);
+
+        if (vid == vdev->vendor_id && did != vdev->device_id) {
+            int i;
+            uint8_t csum, *data = vdev->rom;
+
+            pci_set_word(vdev->rom + pci_get_word(vdev->rom + 0x18) + 6,
+                         vdev->device_id);
+            data[6] = 0;
+
+            for (csum = 0, i = 0; i < vdev->rom_size; i++) {
+                csum += data[i];
+            }
+
+            data[6] = -csum;
+        }
+    }
 }
 
 static uint64_t vfio_rom_read(void *opaque, hwaddr addr, unsigned size)