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Message-ID: <73d47a53-3146-6719-ec20-39a5633350fa@arm.com>
Date: Fri, 27 Jan 2017 17:50:14 +0000
From: Robin Murphy <robin.murphy@....com>
To: Geert Uytterhoeven <geert+renesas@...der.be>,
Joerg Roedel <joro@...tes.org>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>
Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>,
Marek Szyprowski <m.szyprowski@...sung.com>,
Magnus Damm <magnus.damm@...il.com>,
iommu@...ts.linux-foundation.org,
linux-arm-kernel@...ts.infradead.org,
linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] iommu/dma: Add support for
DMA_ATTR_FORCE_CONTIGUOUS
Hi Geert,
On 27/01/17 15:34, Geert Uytterhoeven wrote:
> Add helpers for allocating physically contiguous DMA buffers to the
> generic IOMMU DMA code. This can be useful when two or more devices
> with different memory requirements are involved in buffer sharing.
>
> The iommu_dma_{alloc,free}_contiguous() functions complement the existing
> iommu_dma_{alloc,free}() functions, and allow architecture-specific code
> to implement support for the DMA_ATTR_FORCE_CONTIGUOUS attribute on
> systems with an IOMMU. As this uses the CMA allocator, setting this
> attribute has a runtime-dependency on CONFIG_DMA_CMA.
>
> Note that unlike the existing iommu_dma_alloc() helper,
> iommu_dma_alloc_contiguous() has no callback to flush pages.
> Ensuring the returned region is made visible to a non-coherent device is
> the responsibility of the caller.
>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> ---
> v2:
> - Provide standalone iommu_dma_{alloc,free}_contiguous() functions, as
> requested by Robin Murphy,
> - Simplify operations by getting rid of the page array/scatterlist
> dance, as the buffer is contiguous,
> - Move CPU cache magement into the caller, which is much simpler with
> a single contiguous buffer.
Thanks for the rework, that's a lot easier to make sense of! Now, please
don't hate me, but...
> ---
> drivers/iommu/dma-iommu.c | 72 +++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/dma-iommu.h | 4 +++
> 2 files changed, 76 insertions(+)
>
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 2db0d641cf4505b5..8f8ed4426f9a3a12 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -30,6 +30,7 @@
> #include <linux/pci.h>
> #include <linux/scatterlist.h>
> #include <linux/vmalloc.h>
> +#include <linux/dma-contiguous.h>
>
> struct iommu_dma_msi_page {
> struct list_head list;
> @@ -408,6 +409,77 @@ struct page **iommu_dma_alloc(struct device *dev, size_t size, gfp_t gfp,
> }
>
> /**
> + * iommu_dma_free_contiguous - Free a buffer allocated by
> + * iommu_dma_alloc_contiguous()
> + * @dev: Device which owns this buffer
> + * @page: Buffer page pointer as returned by iommu_dma_alloc_contiguous()
> + * @size: Size of buffer in bytes
> + * @handle: DMA address of buffer
> + *
> + * Frees the pages associated with the buffer.
> + */
> +void iommu_dma_free_contiguous(struct device *dev, struct page *page,
> + size_t size, dma_addr_t *handle)
> +{
> + __iommu_dma_unmap(iommu_get_domain_for_dev(dev), *handle);
> + dma_release_from_contiguous(dev, page, PAGE_ALIGN(size) >> PAGE_SHIFT);
> + *handle = DMA_ERROR_CODE;
> +}
> +
> +/**
> + * iommu_dma_alloc_contiguous - Allocate and map a buffer contiguous in IOVA
> + * and physical space
> + * @dev: Device to allocate memory for. Must be a real device attached to an
> + * iommu_dma_domain
> + * @size: Size of buffer in bytes
> + * @prot: IOMMU mapping flags
> + * @handle: Out argument for allocated DMA handle
> + *
> + * Return: Buffer page pointer, or NULL on failure.
> + *
> + * Note that unlike iommu_dma_alloc(), it's the caller's responsibility to
> + * ensure the returned region is made visible to the given non-coherent device.
> + */
> +struct page *iommu_dma_alloc_contiguous(struct device *dev, size_t size,
> + int prot, dma_addr_t *handle)
> +{
> + struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
> + struct iova_domain *iovad = cookie_iovad(domain);
> + dma_addr_t dma_addr;
> + unsigned int count;
> + struct page *page;
> + struct iova *iova;
> + int ret;
> +
> + *handle = DMA_ERROR_CODE;
> +
> + size = PAGE_ALIGN(size);
> + count = size >> PAGE_SHIFT;
> + page = dma_alloc_from_contiguous(dev, count, get_order(size));
> + if (!page)
> + return NULL;
> +
> + iova = __alloc_iova(domain, size, dev->coherent_dma_mask);
> + if (!iova)
> + goto out_free_pages;
> +
> + size = iova_align(iovad, size);
> + dma_addr = iova_dma_addr(iovad, iova);
> + ret = iommu_map(domain, dma_addr, page_to_phys(page), size, prot);
> + if (ret < 0)
> + goto out_free_iova;
> +
> + *handle = dma_addr;
> + return page;
> +
> +out_free_iova:
> + __free_iova(iovad, iova);
> +out_free_pages:
> + dma_release_from_contiguous(dev, page, count);
> + return NULL;
> +}
...now that I can see it clearly, isn't this more or less just:
page = dma_alloc_from_contiguous(dev, ...);
if (page)
dma_addr = iommu_dma_map_page(dev, page, ...);
?
Would it not be even simpler to just make those two calls directly from
the arm64 code?
Robin.
> +
> +/**
> * iommu_dma_mmap - Map a buffer into provided user VMA
> * @pages: Array representing buffer from iommu_dma_alloc()
> * @size: Size of buffer in bytes
> diff --git a/include/linux/dma-iommu.h b/include/linux/dma-iommu.h
> index 7f7e9a7e3839966c..7eee62c2b0e752f7 100644
> --- a/include/linux/dma-iommu.h
> +++ b/include/linux/dma-iommu.h
> @@ -45,6 +45,10 @@ struct page **iommu_dma_alloc(struct device *dev, size_t size, gfp_t gfp,
> void (*flush_page)(struct device *, const void *, phys_addr_t));
> void iommu_dma_free(struct device *dev, struct page **pages, size_t size,
> dma_addr_t *handle);
> +struct page *iommu_dma_alloc_contiguous(struct device *dev, size_t size,
> + int prot, dma_addr_t *handle);
> +void iommu_dma_free_contiguous(struct device *dev, struct page *page,
> + size_t size, dma_addr_t *handle);
>
> int iommu_dma_mmap(struct page **pages, size_t size, struct vm_area_struct *vma);
>
>
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