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-rw-r--r--hw/nvram/fw_cfg.c4
-rw-r--r--include/hw/nvram/fw_cfg.h3
2 files changed, 6 insertions, 1 deletions
diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
index f3acb47..7866248 100644
--- a/hw/nvram/fw_cfg.c
+++ b/hw/nvram/fw_cfg.c
@@ -32,7 +32,6 @@
#include "qemu/error-report.h"
#include "qemu/config-file.h"
-#define FW_CFG_CTL_SIZE 2
#define FW_CFG_NAME "fw_cfg"
#define FW_CFG_PATH "/machine/" FW_CFG_NAME
@@ -886,6 +885,9 @@ static void fw_cfg_io_realize(DeviceState *dev, Error **errp)
FWCfgIoState *s = FW_CFG_IO(dev);
SysBusDevice *sbd = SYS_BUS_DEVICE(dev);
+ /* when using port i/o, the 8-bit data register ALWAYS overlaps
+ * with half of the 16-bit control register. Hence, the total size
+ * of the i/o region used is FW_CFG_CTL_SIZE */
memory_region_init_io(&s->comb_iomem, OBJECT(s), &fw_cfg_comb_mem_ops,
FW_CFG(s), "fwcfg", FW_CFG_CTL_SIZE);
sysbus_add_io(sbd, s->iobase, &s->comb_iomem);
diff --git a/include/hw/nvram/fw_cfg.h b/include/hw/nvram/fw_cfg.h
index 5d19975..4315f4e 100644
--- a/include/hw/nvram/fw_cfg.h
+++ b/include/hw/nvram/fw_cfg.h
@@ -44,6 +44,9 @@
#define FW_CFG_INVALID 0xffff
+/* width in bytes of fw_cfg control register */
+#define FW_CFG_CTL_SIZE 0x02
+
#define FW_CFG_MAX_FILE_PATH 56
#ifndef NO_QEMU_PROTOS
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