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Re: [Libreboot] message during boot: "DMAR: Failed to map dmar2"
From: |
Bruno Dantas |
Subject: |
Re: [Libreboot] message during boot: "DMAR: Failed to map dmar2" |
Date: |
Thu, 12 Nov 2015 08:25:59 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Icedove/38.3.0 |
It seems that interrupt mapping is done by BIOS (or Libreboot in my case)
first, then the linux kernel remaps things for whatever reason [0]. I know
nothing about this low-level stuff, but because the laptop is working despite
the DMAR failure, I ventured a guess that the interrupt remapping done by the
kernel is not strictly necessary.
Therefore, I looked at the complete list of kernel boot parameters [1] and
tried all the ones that sounded promising. I found that intremap=off makes the
boot-time DMAR error go away! I tested all peripherals and everything seems to
be working fine. Relevant lines from dmesg here: http://pastebin.com/KCGVaf8U
In some cases, this DMAR error is related to faulty chipsets [2]. I guess the
question that remains is whether my T400 (or its Libreboot) is defective in
some way or is the DMAR failure something that is expected to happen on every
T400 with Libreboot? If there is nothing wrong with my hardware or my Libreboot
flash, is booting with intremap=off ill-advised for any reason?
[0]
https://unix.stackexchange.com/questions/84880/what-is-meant-by-interrupt-remapping-in-linux
[1] https://www.kernel.org/doc/Documentation/kernel-parameters.txt
[2] https://www.netiq.com/support/kb/doc.php?id=7014344