[Qemu-devel] [PATCH v6 6/8] acpi: fix "Memory device control fields" register

[Zhu Guihua]

acpi_mem_hotplug.txt states that 0 bit in Memory device control fields
must be cleared before writing to register. Now "Memory device control
fields" is declared with "Preserve" update rule, so 0 bit isn't cleared
when other fields are written.

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

Signed-off-by: Zhu Guihua <address@hidden>
---
 docs/specs/acpi_mem_hotplug.txt | 5 ++++-
 hw/i386/acpi-build.c            | 2 +-
 2 files changed, 5 insertions(+), 2 deletions(-)

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
diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index dc1b8e8..eb66fef 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -924,7 +924,7 @@ 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));
-- 
1.9.3