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SubjectRe: [PATCH 07/21] dma-iommu: move the arm64 wrappers to common code
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On 27/03/2019 08:04, Christoph Hellwig wrote:
[...]
> @@ -649,19 +696,44 @@ static dma_addr_t __iommu_dma_map(struct device *dev, phys_addr_t phys,
> return iova + iova_off;
> }
>
> -dma_addr_t iommu_dma_map_page(struct device *dev, struct page *page,
> +static dma_addr_t __iommu_dma_map_page(struct device *dev, struct page *page,
> unsigned long offset, size_t size, int prot)
> {
> return __iommu_dma_map(dev, page_to_phys(page) + offset, size, prot,
> iommu_get_dma_domain(dev));
> }
>
> -void iommu_dma_unmap_page(struct device *dev, dma_addr_t handle, size_t size,
> - enum dma_data_direction dir, unsigned long attrs)
> +static void __iommu_dma_unmap_page(struct device *dev, dma_addr_t handle,
> + size_t size, enum dma_data_direction dir, unsigned long attrs)
> {
> __iommu_dma_unmap(iommu_get_dma_domain(dev), handle, size);
> }
>
> +static dma_addr_t iommu_dma_map_page(struct device *dev, struct page *page,
> + unsigned long offset, size_t size, enum dma_data_direction dir,
> + unsigned long attrs)
> +{
> + phys_addr_t phys = page_to_phys(page) + offset;
> + bool coherent = dev_is_dma_coherent(dev);
> + dma_addr_t dma_handle;
> +
> + dma_handle =__iommu_dma_map(dev, phys, size,
> + dma_info_to_prot(dir, coherent, attrs),
> + iommu_get_dma_domain(dev));
> + if (!coherent && !(attrs & DMA_ATTR_SKIP_CPU_SYNC) &&
> + dma_handle != DMA_MAPPING_ERROR)
> + arch_sync_dma_for_device(dev, phys, size, dir);
> + return dma_handle;
> +}
> +
> +static void iommu_dma_unmap_page(struct device *dev, dma_addr_t dma_handle,
> + size_t size, enum dma_data_direction dir, unsigned long attrs)
> +{
> + if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
> + iommu_dma_sync_single_for_cpu(dev, dma_handle, size, dir);
> + __iommu_dma_unmap(iommu_get_domain_for_dev(dev), dma_handle, size);

That wants to be iommu_get_dma_domain() there to minimise the overhead.
In fact, I guess this could now be streamlined a bit in the style of
iommu_dma_map_page() above - i.e. avoid doing a second domain lookup in
the sync case - but that can happen later (if indeed you haven't already).

> +}
> +
> /*
> * Prepare a successfully-mapped scatterlist to give back to the caller.
> *

[...]

> @@ -843,12 +923,257 @@ dma_addr_t iommu_dma_map_resource(struct device *dev, phys_addr_t phys,
> iommu_get_dma_domain(dev));
> }
>
> -void iommu_dma_unmap_resource(struct device *dev, dma_addr_t handle,
> +static void iommu_dma_unmap_resource(struct device *dev, dma_addr_t handle,
> size_t size, enum dma_data_direction dir, unsigned long attrs)
> {
> __iommu_dma_unmap(iommu_get_dma_domain(dev), handle, size);
> }
>
> +static void *iommu_dma_alloc(struct device *dev, size_t size,
> + dma_addr_t *handle, gfp_t gfp, unsigned long attrs)
> +{
> + bool coherent = dev_is_dma_coherent(dev);
> + int ioprot = dma_info_to_prot(DMA_BIDIRECTIONAL, coherent, attrs);
> + size_t iosize = size;
> + void *addr;
> +
> + size = PAGE_ALIGN(size);
> +
> + /*
> + * Some drivers rely on this, and we probably don't want the
> + * possibility of stale kernel data being read by devices anyway.
> + */

That comment can probably be dropped now that zeroing is official API
behaviour.

> + gfp |= __GFP_ZERO;

[...]

> +/*
> + * The IOMMU core code allocates the default DMA domain, which the underlying
> + * IOMMU driver needs to support via the dma-iommu layer.
> + */
> +void iommu_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
> + const struct iommu_ops *ops)

There's really no need to even pass @ops in here - in the existing arm64
logic it's merely a token representing "should I do IOMMU setup?", and
after this refactoring that's already been decided by our caller here.

> +{
> + struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
> +
> + if (!domain || domain->type != IOMMU_DOMAIN_DMA)

This change means we now spam the logs with spurious warnings when
configured for passthrough, which is not what we want.

> + goto out_err;
> + if (iommu_dma_init_domain(domain, dma_base, size, dev))
> + goto out_err;
> +
> + dev->dma_ops = &iommu_dma_ops;
> + return;
> +out_err:
> + pr_warn("Failed to set up IOMMU for device %s; retaining platform DMA ops\n",
> + dev_name(dev));
> +}
> +
> static struct iommu_dma_msi_page *iommu_dma_get_msi_page(struct device *dev,
> phys_addr_t msi_addr, struct iommu_domain *domain)
> {
> @@ -921,3 +1246,5 @@ void iommu_dma_map_msi_msg(int irq, struct msi_msg *msg)
> msg->address_lo += lower_32_bits(msi_page->iova);
> }
> }
> +
> +arch_initcall(iova_cache_get);

This feels a bit funky - TBH I'd rather just keep iommu_dma_init()
around and make it static, if only for the sake of looking "normal".

[...]
> -static inline int iommu_dma_init(void)
> +static inline void iommu_setup_dma_ops(struct device *dev, u64 dma_base,
> + u64 size, const struct iommu_ops *ops)
> {
> - return 0;
> }

I don't think it makes sense to have a stub for that - AFAICS it should
only ever be called form arch code with an inherent "select IOMMU_DMA"
(much like the stuff which isn't stubbed currently).

Otherwise, I'm about 97% sure the rest of the move looks OK - thanks for
splitting things up.

Robin.

>
> static inline int iommu_get_dma_cookie(struct iommu_domain *domain)
>

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