linux-kernel - Re: [PATCH 9/9] x86/iommu: use dma_ops_list in get_dma

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Date:	Fri, 26 Sep 2008 13:26:19 +0530
From:	Amit Shah <amit.shah@...hat.com>
To:	Joerg Roedel <joerg.roedel@....com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	iommu@...ts.linux-foundation.org,
	David Woodhouse <dwmw2@...radead.org>,
	Muli Ben-Yehuda <muli@...ibm.com>,
	Ingo Molnar <mingo@...hat.com>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Subject: Re: [PATCH 9/9] x86/iommu: use dma_ops_list in get_dma_ops

* On Monday 22 Sep 2008 23:51:21 Joerg Roedel wrote:
> This patch enables stackable dma_ops on x86. To do this, it also enables
> the per-device dma_ops on i386.
>
> Signed-off-by: Joerg Roedel <joerg.roedel@....com>
> ---
>  arch/x86/kernel/pci-dma.c     |   26 ++++++++++++++++++++++++++
>  include/asm-x86/device.h      |    6 +++---
>  include/asm-x86/dma-mapping.h |   14 +++++++-------
>  3 files changed, 36 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
> index b990fb6..2e517c2 100644
> --- a/arch/x86/kernel/pci-dma.c
> +++ b/arch/x86/kernel/pci-dma.c
> @@ -82,6 +82,32 @@ void x86_register_dma_ops(struct dma_mapping_ops *ops,
>  	write_unlock_irqrestore(&dma_ops_list_lock, flags);
>  }
>
> +struct dma_mapping_ops *find_dma_ops_for_device(struct device *dev)
> +{
> +	int i;
> +	unsigned long flags;
> +	struct dma_mapping_ops *entry, *ops = NULL;
> +
> +	read_lock_irqsave(&dma_ops_list_lock, flags);
> +
> +	for (i = 0; i < DMA_OPS_TYPE_MAX; ++i)
> +		list_for_each_entry(entry, &dma_ops_list[i], list) {
> +			if (!entry->device_supported)
> +				continue;
> +			if (entry->device_supported(dev)) {
> +				ops = entry;
> +				goto out;
> +			}
> +		}
> +out:
> +	read_unlock_irqrestore(&dma_ops_list_lock, flags);

For PVDMA, we want the "native" dma_ops to succeed first, eg, nommu, and then 
do our "PV DMA", which is just translating gpa  to hpa and then program the 
hardware. This isn't being done here. This can be done by extending the 
return type:

DMA_DEV_NOT_SUPPORTED
DMA_DEV_HANDLED
DMA_DEV_PASS

Where NOT_SUPPORTED means we should look for the next one in the chain 
(current return value 0), DEV_HANDLED means the dma operation has been 
handled successfully (current return value 1) and DEV_PASS means fall back to 
the next layer and then return back.

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