linux-kernel - Re: [RFC patch] init default dma_ops to prepare intel_iommu

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Date:	Thu, 13 Aug 2009 13:49:27 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	fenghua.yu@...el.com
Cc:	luming.yu@...il.com, dwmw2@...radead.org, tony.luck@...el.com,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [RFC patch] init default dma_ops to prepare intel_iommu_init
 failure

On Wed, 12 Aug 2009 11:17:22 -0700
Fenghua Yu <fenghua.yu@...el.com> wrote:

> > Hi there,
> > 
> > On ia64 platform with dmar table and new upstream
> > kernel(config_dmar_default_on enabled),
> > if intel_iommu_init ends up without dma_ops initialized or other iommu
> > failures.
> > We got nothing to fall back. The following patch fixes it.
> > 
> x86/x86-64 also needs this fix. Please check the pci_swiotlb_init for x86/64.

x86 falls back into nommu_dam_ops (though it would be better to use
swiotlb on x86_64).


> > Please review. If make sense, please apply.
> > 
> > **The patch is enclosed in text attachment*
> > **Using web client to send the patch* *
> > **below is for review, please apply attached  patch*/
> > 
> > Thanks,
> > Luming
> > 
> > Signed-off-by: Yu Luming <luming.yu@...el.com>
> > 
> > arch/ia64/kernel/pci-swiotlb.c |   14 ++++++--------
> >  1 file changed, 6 insertions(+), 8 deletions(-)
> > 
> > diff --git a/arch/ia64/kernel/pci-swiotlb.c b/arch/ia64/kernel/pci-swiotlb.c
> > index 223abb1..d5dcaf5 100644
> > --- a/arch/ia64/kernel/pci-swiotlb.c
> > +++ b/arch/ia64/kernel/pci-swiotlb.c
> > @@ -46,15 +46,13 @@ void __init swiotlb_dma_init(void)
> > 
> >  void __init pci_swiotlb_init(void)
> >  {
> > -	if (!iommu_detected || iommu_pass_through) {
> 
> This check can not be removed. Otherwise, swiotlb_dma_ops will always override
> previous dma_ops value.

Yeah.


> I think you can change this check to something like:
> 	if (!dma_ops || iommu_pass_through) {

I don't think this work since pci_iommu_alloc() always sets up dma_ops
and calls pci_swiotlb_init().

All we need to do here is calling swiotlb_init() then we can use
swiotlb_dma_ops after intel_iommu_init() fails:

http://marc.info/?l=linux-kernel&m=125013354518721&w=2


> With this change, checking iommu_detected is unnecesary because checking dma_ops
> covers it.
> 
> >  #ifdef CONFIG_IA64_GENERIC
> > -		swiotlb = 1;
> > -		printk(KERN_INFO "PCI-DMA: Re-initialize machine vector.\n");
> > -		machvec_init("dig");
> > -		swiotlb_init();
> > -		dma_ops = &swiotlb_dma_ops;
> > +	swiotlb = 1;
> > +	printk(KERN_INFO "PCI-DMA: Re-initialize machine vector.\n");
> > +	machvec_init("dig");
> > +	swiotlb_init();
> > +	dma_ops = &swiotlb_dma_ops;
> >  #else
> > -		panic("Unable to find Intel IOMMU");
> > +	panic("Unable to find Intel IOMMU");
> >  #endif
> > -	}
> >  }
> 
> 
> 
> --
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