Re: [PATCH v8 1/4] firmware: introduce sysfs driver for QEMU's fw_cfg device

On Sun, Feb 21, 2016 at 08:06:17AM -0500, Gabriel L. Somlo wrote:

quoted

quoted

+#if !(defined(FW_CFG_CTRL_OFF) && defined(FW_CTRL_DATA_OFF))
+# if (defined(CONFIG_ARM) || defined(CONFIG_ARM64))
+#  define FW_CFG_CTRL_OFF 0x08
+#  define FW_CFG_DATA_OFF 0x00
+# elif (defined(CONFIG_PPC_PMAC) || defined(CONFIG_SPARC32)) /* ppc/mac,sun4m */
+#  define FW_CFG_CTRL_OFF 0x00
+#  define FW_CFG_DATA_OFF 0x02
+# elif (defined(CONFIG_X86) || defined(CONFIG_SPARC64)) /* x86, sun4u */
+#  define FW_CFG_CTRL_OFF 0x00
+#  define FW_CFG_DATA_OFF 0x01
+# else
+#  warning "QEMU FW_CFG may not be available on this architecture!"
+#  define FW_CFG_CTRL_OFF 0x00
+#  define FW_CFG_DATA_OFF 0x01

Better not try hacks like this, they are hard
to support down the road. Please only list what is tested and
actually exposed by QEMU.

I was looking for a standard way to advertise register offsets within
the ioport or mmio region assigned to fw_cfg, but right now the answer
is "there isn't one", and "register offsets are an arch specific
detail". As such, the only reasonable way I saw was to copy the same
values used in the QEMU source.

See also:
https://lists.gnu.org/archive/html/qemu-devel/2015-11/msg05037.html
 
Thanks much,
--Gabriel

My point is you don't know what will qemu do on these
other arches which do not at the moment have fw cfg.
So don't try to guess!

-- 
MST