[Qemu-devel] [PATCH v4 1/5] fw_cfg: expose control register size in fw_cfg.h

["Gabriel L. Somlo" <somlo@cmu.edu>]

Expose the size of the control register (FW_CFG_SIZE, renamed to
FW_CFG_CTL_SIZE) in fw_cfg.h.
Add comment to fw_cfg_io_realize() pointing out that since the
8-bit data register is always subsumed by the 16-bit control
register in the port I/O case, we use the control register width
as the *total* width of the port I/O region reserved for the device.

Suggested-by: Marc Marí <markmb@redhat.com>
Signed-off-by: Gabriel Somlo <somlo@cmu.edu>
---
 hw/nvram/fw_cfg.c         | 8 +++++---
 include/hw/nvram/fw_cfg.h | 3 +++
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
index 658f8c4..9dd95c7 100644
--- a/hw/nvram/fw_cfg.c
+++ b/hw/nvram/fw_cfg.c
@@ -30,7 +30,6 @@
 #include "qemu/error-report.h"
 #include "qemu/config-file.h"
 
-#define FW_CFG_SIZE 2
 #define FW_CFG_NAME "fw_cfg"
 #define FW_CFG_PATH "/machine/" FW_CFG_NAME
 
@@ -672,8 +671,11 @@ 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_SIZE);
+                          FW_CFG(s), "fwcfg", FW_CFG_CTL_SIZE);
     sysbus_add_io(sbd, s->iobase, &s->comb_iomem);
 }
 
@@ -705,7 +707,7 @@ static void fw_cfg_mem_realize(DeviceState *dev, Error **errp)
     const MemoryRegionOps *data_ops = &fw_cfg_data_mem_ops;
 
     memory_region_init_io(&s->ctl_iomem, OBJECT(s), &fw_cfg_ctl_mem_ops,
-                          FW_CFG(s), "fwcfg.ctl", FW_CFG_SIZE);
+                          FW_CFG(s), "fwcfg.ctl", FW_CFG_CTL_SIZE);
     sysbus_init_mmio(sbd, &s->ctl_iomem);
 
     if (s->data_width > data_ops->valid.max_access_size) {
diff --git a/include/hw/nvram/fw_cfg.h b/include/hw/nvram/fw_cfg.h
index e60d3ca..5008270 100644
--- a/include/hw/nvram/fw_cfg.h
+++ b/include/hw/nvram/fw_cfg.h
@@ -46,6 +46,9 @@
 
 #define FW_CFG_INVALID          0xffff
 
+/* width in bytes of fw_cfg control port */
+#define FW_CFG_CTL_SIZE         0x02
+
 #define FW_CFG_MAX_FILE_PATH    56
 
 #ifndef NO_QEMU_PROTOS
-- 
2.4.3