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RE: [PATCHv8 10/10] ARM: dma-mapping: add support for IOMMU mapper



Hi Arnd,

On Tuesday, April 10, 2012 1:58 PM Arnd Bergmann wrote:

> On Tuesday 10 April 2012, Marek Szyprowski wrote:
> > +/**
> > + * arm_iommu_create_mapping
> > + * @bus: pointer to the bus holding the client device (for IOMMU calls)
> > + * @base: start address of the valid IO address space
> > + * @size: size of the valid IO address space
> > + * @order: accuracy of the IO addresses allocations
> > + *
> > + * Creates a mapping structure which holds information about used/unused
> > + * IO address ranges, which is required to perform memory allocation and
> > + * mapping with IOMMU aware functions.
> > + *
> > + * The client device need to be attached to the mapping with
> > + * arm_iommu_attach_device function.
> > + */
> > +struct dma_iommu_mapping *
> > +arm_iommu_create_mapping(struct bus_type *bus, dma_addr_t base, size_t size,
> > +                        int order)
> > +{
> > +       unsigned int count = size >> (PAGE_SHIFT + order);
> > +       unsigned int bitmap_size = BITS_TO_LONGS(count) * sizeof(long);
> > +       struct dma_iommu_mapping *mapping;
> > +       int err = -ENOMEM;
> > +
> > +       if (!count)
> > +               return ERR_PTR(-EINVAL);
> > +
> > +       mapping = kzalloc(sizeof(struct dma_iommu_mapping), GFP_KERNEL);
> > +       if (!mapping)
> > +               goto err;
> > +
> > +       mapping->bitmap = kzalloc(bitmap_size, GFP_KERNEL);
> > +       if (!mapping->bitmap)
> > +               goto err2;
> > +
> > +       mapping->base = base;
> > +       mapping->bits = BITS_PER_BYTE * bitmap_size;
> > +       mapping->order = order;
> > +       spin_lock_init(&mapping->lock);
> > +
> > +       mapping->domain = iommu_domain_alloc(bus);
> > +       if (!mapping->domain)
> > +               goto err3;
> > +
> > +       kref_init(&mapping->kref);
> > +       return mapping;
> > +err3:
> > +       kfree(mapping->bitmap);
> > +err2:
> > +       kfree(mapping);
> > +err:
> > +       return ERR_PTR(err);
> > +}
> > +EXPORT_SYMBOL(arm_iommu_create_mapping);
> 
> I don't understand this function, mostly I guess because you have not
> provided any users. A few questions here:
> 
> * What is ARM specific about it that it is named arm_iommu_create_mapping?
>   Isn't this completely generic, at least on the interface side?
> 
> * Why is this exported to modules? Which device drivers do you expect
>   to call it?
> 
> * Why do you pass the bus_type in here? That seems like the completely
>   wrong thing to do when all devices are on the same bus type (e.g.
>   amba or platform) but are connected to different instances that each
>   have their own iommu. I guess this is a question for Jörg, because the
>   base iommu interface provides iommu_domain_alloc().

I will soon post a patch which shows how my IOMMU aware dma-mapping 
integrates with Samsung Exynos4 SYSMMU driver, so I will be able to answer
all your questions by pointing to the respective lines in either IOMMU
framework or my integration code.

Best regards
-- 
Marek Szyprowski
Samsung Poland R&D Center


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