Re: [RFC PATCH v2 2/3] arm64: add IOMMU dma_ops

[Yong Wu <yong.wu@mediatek.com>]

On Mon, 2015-02-16 at 20:04 +0000, Robin Murphy wrote:

> >       2)int (*domain_init)(struct iommu_domain *domain);
> >         About this function, it will alloc pagetable for the iommu
> > domain. And We expect the pagetable memory is uncacheable, so try to
> > call "dma_alloc_coherent", unfortunately the "struct device *" can't be
> > passed into this function. so is it possible if adding a parameter in
> > this function.
> 
> ...one of the ideas of the new of_iommu_configure framework is that 
> iommu_ops structures can represent individual IOMMU devices if 
> necessary. The ops->priv pointer was included for that purpose, but 
> isn't very clean so Will has plans to remove it again - it's easy enough 
> to achieve the same effect by having the driver embed the ops in its 
> private instance data instead. I've done that with the ARM SMMU driver 
> which has a similar issue of needing hardware details at domain_init() 
> time (no patches ready yet but I have an iommu/dev branch on top of the 
> iommu/dma branch with some current work-in-progress bits)
> 
> Thanks,
> Robin.
> 
Dear Robin,
        Thanks very much for your suggestion.

        I have a more question: how to do cache maintenance in arm64.

        a) "__dma_flush_range" can not be expected to used directly.
        b) Following Documentation\DMA-API.txt, section: Streaming DMA
mappings. dma_map_single should be used, But I am not sure how to pass
the first "struct device *".
         We have a device which call arch_setup_dma_ops to create the
iommu domain, if we use this device, it will enter __iommu_map_page;
        If we input NULL for dmap_map_single, it will assert at
dma_capable in swiotlb_map_page...

        And normally, we always need do cache maintenance only for some
bytes in the pagetable but not whole a page. Then is there a easy way to
do the cache maintenance?