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

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Message-ID: <20091125101757.GC20489@8bytes.org>
Date:	Wed, 25 Nov 2009 11:17:57 +0100
From:	Joerg Roedel <joro@...tes.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>, mingo@...e.hu,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -tip] x86: fix iommu=soft boot option

On Tue, Nov 24, 2009 at 03:55:03PM -0800, Yinghai Lu wrote:
> FUJITA Tomonori wrote:
> > "x86: Handle HW IOMMU initialization failure gracefully" patchset
> > handled this option properly however somehow I broke it during cleanup
> > after that. Sorry.
> > 
> > =
> > From: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
> > Subject: [PATCH -tip] x86: fix iommu=soft boot option
> > 
> > iommu=soft boot option forces the kernel to use swiotlb.
> > 
> > Signed-off-by: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
> > ---
> >  arch/x86/kernel/pci-swiotlb.c |    4 +++-
> >  1 files changed, 3 insertions(+), 1 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/pci-swiotlb.c b/arch/x86/kernel/pci-swiotlb.c
> > index e36e71d..e3c0a66 100644
> > --- a/arch/x86/kernel/pci-swiotlb.c
> > +++ b/arch/x86/kernel/pci-swiotlb.c
> > @@ -50,6 +50,8 @@ static struct dma_map_ops swiotlb_dma_ops = {
> >   */
> >  int __init pci_swiotlb_init(void)
> >  {
> > +	int use_swiotlb = swiotlb | swiotlb_force;
> > +
> >  	/* don't initialize swiotlb if iommu=off (no_iommu=1) */
> >  #ifdef CONFIG_X86_64
> >  	if (!no_iommu && max_pfn > MAX_DMA32_PFN)
> > @@ -63,5 +65,5 @@ int __init pci_swiotlb_init(void)
> >  		dma_ops = &swiotlb_dma_ops;
> >  	}
> >  
> > -	return swiotlb_force;
> > +	return use_swiotlb;
> >  }
> 
> before your cleanup patchset:
> for AMD 64bit, MEM > 4g, no AGP, iommu=soft
> 1. if BIOS have correct gart setting, Kernel will use gart
> 2. if BIOS does not have correct gart setting, Kernel will use swiotlb
> 
> for AMD 64bit, MEM > 4g, no AGP, no "iommu=soft"
> 1. if BIOS have correct gart setting, Kernel will use gart
> 2. if BIOS does not have correct gart setting, Kernel will allocate some RAM, and set range in AMD NB, and use gart iommu

The swiotlb is used as a dma-api backend always when 'iommu=soft' is specified,
at least the code I read without the cleanup patchset. The cleanup patchset
broke that in some places. Now I need to pass swiotlb=force to achieve the same
for AMD IOMMU. The above patch fixes this.
But that iommu=soft will prevent the kernel from fixing up broken gart settings
is new to me. Where have you seen this behavior?

	Joerg

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