linux-kernel - Re: 2.6.25 DMA: Out of SW-IOMMU space

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Message-ID: <87wshza4oo.fsf@jondo.cante.net>
Date:	Sat, 30 Aug 2008 00:31:51 +0300
From:	Jari Aalto <jari.aalto@...te.net>
To:	linux-kernel@...r.kernel.org
Cc:	Gerardo Exequiel Pozzi <vmlinuz386@...oo.com.ar>
Subject: Re: 2.6.25 DMA: Out of SW-IOMMU space - Asus M2N32 AMD 8GB memory

Gerardo Exequiel Pozzi <vmlinuz386@...oo.com.ar> writes:

>>    REF: http://article.gmane.org/gmane.linux.kernel/725293 (thread >start)
>>
>>but I'll try that once more with this 2.6.26 kernel to double check.
>
> You have mixed options for "swiotlb" and "amd gart", see the
> Documentation/x86_64/boot-options.txt

It's difficult to find the pointer that could explain the correct use of
the options and their combinations.

> iommu=soft,memaper=3 swiotlb=65536 BAD.
>
> memaper=3 don't have any effects here, memaper is only for "AMD GART"
>
> The noagp option in this motherboard is redundant.
>
> iommu=noagp,noaperture,off swiotlb=512M BAD combination options!
> OFF, OFF, OFF, ON: The result are unknown.
>
> You need to use the IOMMU (from AMD GART) that with your options: you
> never used.
>
> When you boot with no iommu options, kernels uses the AMD GART in this
> system, with an aperture of 64MB (too small) to fix, you need only one
> option: iommu=memaper=3

This sort of advice wouldbe wonderful if it wereincluded in the spec,
which as of now is too technical for mere mortals:

    http://www.mjmwired.net/kernel/Documentation/x86_64/boot-options.txt

I'm not surprised that end user cannot know what combination of options
make or does not make sense. I'll try at next boot with plain:

    iommu=memaper=3

Thank you,
Jari
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