Problem writing to ACPI non-volatile memory with /dev/mem - Bad address

Colin Law clanlaw at
Wed Aug 15 08:21:47 UTC 2012

Any thoughts on this from any of the whiz kids out there?  Or anyone
else for that matter.

Perhaps I should report it as a bug on the kernel (never reported a
bug on the kernel yet) and wait for someone to tell me what an idiot I


On 13 August 2012 14:17, Colin Law <clanlaw at> wrote:
> I am trying to implement the workaround for bug #806032 [1] (Fn +
> F[89] does not work for controlling brightness on Clevo laptops) which
> uses a script that writes to the ACPI non-volatile storage using
> /dev/mem.  This works on Oneiric 64 bit kernel 3.0.0-12-generic, but
> not on the 32 bit version of that kernel, nor on the Precise or
> Quantal 32 bit kernels (I don't know yet about the 64 bit version,
> downloading the live CD overnight tonight).  The command I am running
> is
> sudo dd if=value_file of=/dev/mem bs=1 seek=3660685688 count=4
> the error is
> dd: writing `/dev/mem': Bad address
> 3660685688 is 0xDA31A178 and
> sudo cat /proc/iomem
> shows
> ...
> da216000-da32bfff : ACPI Non-volatile Storage
> ...
> As I said, this works ok on the 64 bit kernel (from Oneiric at least).
> Any ideas anyone?
> Colin
> [1]

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