pci: make command SERR bit writable

pcie aer needs SERR bit to be writable, and the PCI spec requires
this as well.  For compatibility, introduce compat global property
command_serr_enable and make this bit readonly for a pre 0.14 pc
machine.
Signed-off-by: NIsaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/pc_piix.c

@@ -217,6 +217,14 @@ static QEMUMachine pc_machine = {
     .desc = "Standard PC",
     .init = pc_init_pci,
     .max_cpus = 255,
+    .compat_props = (GlobalProperty[]) {
+        {
+            .driver   = "PCI",
+            .property = "command_serr_enable",
+            .value    = "off",
+        },
+        { /* end of list */ }
+    },
     .is_default = 1,
 };
 
@@ -265,6 +273,10 @@ static QEMUMachine pc_machine_v0_12 = {
             .driver   = "vmware-svga",
             .property = "rombar",
             .value    = stringify(0),
+        },{
+            .driver   = "PCI",
+            .property = "command_serr_enable",
+            .value    = "off",
         },
         { /* end of list */ }
     }
@@ -300,6 +312,10 @@ static QEMUMachine pc_machine_v0_11 = {
             .driver   = "PCI",
             .property = "rombar",
             .value    = stringify(0),
+        },{
+            .driver   = "PCI",
+            .property = "command_serr_enable",
+            .value    = "off",
         },
         { /* end of list */ }
     }
@@ -347,6 +363,10 @@ static QEMUMachine pc_machine_v0_10 = {
             .driver   = "PCI",
             .property = "rombar",
             .value    = stringify(0),
+        },{
+            .driver   = "PCI",
+            .property = "command_serr_enable",
+            .value    = "off",
         },
         { /* end of list */ }
     },

hw/pci.c

@@ -57,6 +57,8 @@ struct BusInfo pci_bus_info = {
         DEFINE_PROP_UINT32("rombar",  PCIDevice, rom_bar, 1),
         DEFINE_PROP_BIT("multifunction", PCIDevice, cap_present,
                         QEMU_PCI_CAP_MULTIFUNCTION_BITNR, false),
+        DEFINE_PROP_BIT("command_serr_enable", PCIDevice, cap_present,
+                        QEMU_PCI_CAP_SERR_BITNR, true),
         DEFINE_PROP_END_OF_LIST()
     }
 };
@@ -568,6 +570,9 @@ static void pci_init_wmask(PCIDevice *dev)
     pci_set_word(dev->wmask + PCI_COMMAND,
                  PCI_COMMAND_IO | PCI_COMMAND_MEMORY | PCI_COMMAND_MASTER |
                  PCI_COMMAND_INTX_DISABLE);
+    if (dev->cap_present & QEMU_PCI_CAP_SERR) {
+        pci_word_test_and_set_mask(dev->wmask + PCI_COMMAND, PCI_COMMAND_SERR);
+    }
 
     memset(dev->wmask + PCI_CONFIG_HEADER_SIZE, 0xff,
            config_size - PCI_CONFIG_HEADER_SIZE);

hw/pci.h

@@ -118,6 +118,10 @@ enum {
     /* multifunction capable device */
 #define QEMU_PCI_CAP_MULTIFUNCTION_BITNR        3
     QEMU_PCI_CAP_MULTIFUNCTION = (1 << QEMU_PCI_CAP_MULTIFUNCTION_BITNR),
+
+    /* command register SERR bit enabled */
+#define QEMU_PCI_CAP_SERR_BITNR 4
+    QEMU_PCI_CAP_SERR = (1 << QEMU_PCI_CAP_SERR_BITNR),
 };
 
 struct PCIDevice {