linux-kernel - Re: [PATCH -tip] x86: fix iommu=soft boot option

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Message-Id: <20091127170347O.fujita.tomonori@lab.ntt.co.jp>
Date:	Fri, 27 Nov 2009 17:06:21 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	yinghai@...nel.org
Cc:	fujita.tomonori@....ntt.co.jp, mingo@...e.hu,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -tip] x86: fix iommu=soft boot option

On Thu, 26 Nov 2009 23:45:33 -0800
Yinghai Lu <yinghai@...nel.org> wrote:

> >> when AMD64 mem > 4g, no AGP, BIOS set all gart iommu on all nodes size to 32M, and enable bit are set.
> > 
> > I have such machine (with sane BIOS).
> > 
> > But if BIOS is broken, early_gart_iommu_check() disables GART_EN bit
> > (bits 0)?
> 
> not for 32M small size.
> 
> that function only clear that bit when different nodes have different setting.
> 
> > 
> >> 1. iommu=soft, will go through POINT A and POINT B
> > 
> > Not always. if aperture_valid() is true, it doesn't go POINT A. My
> > GART machine doesn't go.
> 
> maybe your bios set GART iommu set to 64M?

Yeah, my machine has sane BIOS.


> >> 2. no "iommu=soft", will go through POINT A and POINT C
> > 
> > As I said, it's not true about POINT A.
> 
> maybe your bios set GART iommu set to 64M?
> 
> > 
> > 
> >> and all will reach POINT X to make sure ENABLE bit is not set.
> > 
> > POINT X doesn't look make sure ENABLE bit is not set. It just fixes up
> > (sets) the address and its size.
> 
>                         write_pci_config(bus, slot, 3, AMD64_GARTAPERTURECTL, aper_order << 1);
> 
> that bit is that bit 0 of AMD64_GARTAPERTURECTL reg.

Oops, thanks.

But as I wrote in the previous mail, can you tell me why we need this?
With 2.6.31 my machine uses swiotlb with GART_EN bit enabled.

My another question is that why can't early_gart_iommu_check()
_always_ disable GART_EN bit?
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