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Date: Thu, 25 Dec 2008 10:53:33 +0100
From: Andre Albsmeier <Andre.Albsmeier@siemens.com>
To: freebsd-hackers@freebsd.org
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Cc: Andre.Albsmeier@siemens.com
Subject: Writing device drivers: How to access a specific memory area?
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X-List-Received-Date: Thu, 25 Dec 2008 09:53:35 -0000

Hello all,

I am writing a driver which needs to access memory at a
specific location. The location depends on what the BIOS
has configured into the host bridge. For example, my
current machine uses an Intel 975X chipset and the memory
location I am interested in has been set to 0xFED14000 and
is 16KB in size (this is MCHBAR of the 975X memory hub).

I have no idea how to access this space from my driver.
I have played around with bus_alloc_resource() but this
only gives me back NULL.

However, a devinfo -r gives me:

nexus0
  npx0
  acpi0
      Interrupt request lines:
          9
      I/O ports:
          0x10-0x1f
...
          0x800-0x87f
      I/O memory addresses:
          0x0-0x9ffff
          0xc0000-0xdffff
          0xe0000-0xfffff
          0x100000-0x7fffffff
          0xf0000000-0xf3ffffff
          0xfec00000-0xfec00fff
          0xfed13000-0xfed19fff		<---
          0xfed1c000-0xfed1ffff
          0xfed20000-0xfed3ffff
          0xfed50000-0xfed8ffff
          0xfee00000-0xfee00fff
          0xffb00000-0xffbfffff
          0xfff00000-0xffffffff
    cpu0
...

The line marked with <--- shows the range which includes
the location I am interested in. It is probably assigned
to the acpi0 device.

How do I proceed from this? Do I have to hack around in
the ACPI-Code? I don't hope so ;-)

I only need access to this memory location during the
probe of my driver to read some configuration data.
I do not need to access it later anymore...

Thanks a lot for any hints,

	-Andre