[v4,1/6] q35: acpi: do not create dummy MCFG table
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Message ID 20190419003053.8260-2-richardw.yang@linux.intel.com
State New
Headers show
Series
  • Extract build_mcfg
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Commit Message

Wei Yang April 19, 2019, 12:30 a.m. UTC
From: Igor Mammedov <imammedo@redhat.com>

Dummy table (with signature "QEMU") creation came from original SeaBIOS
codebase. And QEMU would have to keep it around if there were Q35 machine
that depended on keeping ACPI tables blob constant size. Luckily there
were no versioned Q35 machine types before commit:
  (since 2.3) a1666142db acpi-build: make ROMs RAM blocks resizeable
which obsoleted need to keep ACPI tables blob the same size on source/destination.

Considering the 1st versioned machine is pc-q35-2.4, the dummy table
is not really necessary and it's safe to drop it without breaking
cross version migration in both directions unconditionally.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 hw/i386/acpi-build.c | 18 ++++--------------
 1 file changed, 4 insertions(+), 14 deletions(-)

Patch
diff mbox series

diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index b17d4a711d..d009176072 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -2401,7 +2401,6 @@  static void
 build_mcfg_q35(GArray *table_data, BIOSLinker *linker, AcpiMcfgInfo *info)
 {
     AcpiTableMcfg *mcfg;
-    const char *sig;
     int len = sizeof(*mcfg) + 1 * sizeof(mcfg->allocation[0]);
 
     mcfg = acpi_data_push(table_data, len);
@@ -2411,19 +2410,7 @@  build_mcfg_q35(GArray *table_data, BIOSLinker *linker, AcpiMcfgInfo *info)
     mcfg->allocation[0].start_bus_number = 0;
     mcfg->allocation[0].end_bus_number = PCIE_MMCFG_BUS(info->mcfg_size - 1);
 
-    /* MCFG is used for ECAM which can be enabled or disabled by guest.
-     * To avoid table size changes (which create migration issues),
-     * always create the table even if there are no allocations,
-     * but set the signature to a reserved value in this case.
-     * ACPI spec requires OSPMs to ignore such tables.
-     */
-    if (info->mcfg_base == PCIE_BASE_ADDR_UNMAPPED) {
-        /* Reserved signature: ignored by OSPM */
-        sig = "QEMU";
-    } else {
-        sig = "MCFG";
-    }
-    build_header(linker, table_data, (void *)mcfg, sig, len, 1, NULL, NULL);
+    build_header(linker, table_data, (void *)mcfg, "MCFG", len, 1, NULL, NULL);
 }
 
 /*
@@ -2592,6 +2579,9 @@  static bool acpi_get_mcfg(AcpiMcfgInfo *mcfg)
     }
     mcfg->mcfg_base = qnum_get_uint(qobject_to(QNum, o));
     qobject_unref(o);
+    if (mcfg->mcfg_base == PCIE_BASE_ADDR_UNMAPPED) {
+        return false;
+    }
 
     o = object_property_get_qobject(pci_host, PCIE_HOST_MCFG_SIZE, NULL);
     assert(o);