[Qemu-devel] [PULL 21/28] acpi: fix "Memory device control fields" register

["Michael S. Tsirkin" <mst@redhat.com>]

From: Zhu Guihua <zhugh.fnst@cn.fujitsu.com>

0 bit in Memory device control fields must be cleared before writing to
register. But now this field isn't cleared when other fields are written.

To solve this bug, This patch fixes UpdateRule to WriteAsZeros in "Memory
device control fields" register.

Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Zhu Guihua <zhugh.fnst@cn.fujitsu.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 hw/i386/acpi-build.c            | 2 +-
 docs/specs/acpi_mem_hotplug.txt | 5 ++++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index 085dc6d..4202d76 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -872,7 +872,7 @@ build_ssdt(GArray *table_data, GArray *linker,
         aml_append(scope, field);
 
         field = aml_field(stringify(MEMORY_HOTPLUG_IO_REGION), aml_byte_acc,
-                          aml_preserve);
+                          aml_write_as_zeros);
         aml_append(field, aml_reserved_field(160 /* bits, Offset(20) */));
         aml_append(field, /* 1 if enabled, read only */
             aml_named_field(stringify(MEMORY_SLOT_ENABLED), 1));
diff --git a/docs/specs/acpi_mem_hotplug.txt b/docs/specs/acpi_mem_hotplug.txt
index dcc4808..68daa14 100644
--- a/docs/specs/acpi_mem_hotplug.txt
+++ b/docs/specs/acpi_mem_hotplug.txt
@@ -31,7 +31,10 @@ Memory hot-plug interface (IO port 0xa00-0xa17, 1-4 byte access):
       [0xc-0x13] reserved, writes into it are ignored
       [0x14] Memory device control fields
           bits:
-              0: reserved, OSPM must clear it before writing to register
+              0: reserved, OSPM must clear it before writing to register.
+                 Due to BUG in versions prior 2.4 that field isn't cleared
+                 when other fields are written. Keep it reserved and don't
+                 try to reuse it.
               1: if set to 1 clears device insert event, set by OSPM
                  after it has emitted device check event for the
                  selected memory device
-- 
MST