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[Qemu-devel] [PULL 1/6] fw_cfg: expose control register size in fw_cfg.h

From: Gerd Hoffmann
Subject: [Qemu-devel] [PULL 1/6] fw_cfg: expose control register size in fw_cfg.h
Date: Tue, 8 Mar 2016 12:18:56 +0100

From: "Gabriel L. Somlo" <address@hidden>

Expose the size of the control register (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 (classic, non-DMA) port I/O region reserved
for the device.

Cc: Marc MarĂ­ <address@hidden>
Signed-off-by: Gabriel Somlo <address@hidden>
Reviewed-by: Laszlo Ersek <address@hidden>
Reviewed-by: Marc MarĂ­ <address@hidden>
Message-id: address@hidden
Signed-off-by: Gerd Hoffmann <address@hidden>
 hw/nvram/fw_cfg.c         | 4 +++-
 include/hw/nvram/fw_cfg.h | 3 +++
 2 files changed, 6 insertions(+), 1 deletion(-)

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 
     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

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