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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:

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?


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