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Re: [PATCH v5 3/9] dma-mapping: add dma_{map,unmap}_resource

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Hi Christoph,

On 2016-03-07 23:38:47 -0800, Christoph Hellwig wrote:
> Please add some documentation on where/how this should be used.  It's
> not a very obvious interface.

Good idea, I have added the following to Documentation/DMA-API.txt and 
folded it in to this patch. Do you feel it's adequate and do you know 
anywhere else I should add documentation?

diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
index 45ef3f2..248556a 100644
--- a/Documentation/DMA-API.txt
+++ b/Documentation/DMA-API.txt
@@ -277,14 +277,29 @@ and <size> parameters are provided to do partial page mapping, it is
 recommended that you never use these unless you really know what the
 cache width is.
 
+dma_addr_t
+dma_map_resource(struct device *dev, phys_addr_t phys_addr, size_t size,
+                enum dma_data_direction dir, struct dma_attrs *attrs)
+
+Maps a MMIO region so it can be accessed by the device and returns the
+DMA address of the memory. API should only be used to map device MMIO,
+mapping of RAM is not permitted.
+
+void
+dma_unmap_resource(struct device *dev, dma_addr_t addr, size_t size,
+                  enum dma_data_direction dir, struct dma_attrs *attrs)
+
+Unmaps the IOMMU region previously mapped. All the parameters passed in
+must be identical to those passed in (and returned) by the mapping API.
+
 int
 dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
 
-In some circumstances dma_map_single() and dma_map_page() will fail to create
-a mapping. A driver can check for these errors by testing the returned
-DMA address with dma_mapping_error(). A non-zero return value means the mapping
-could not be created and the driver should take appropriate action (e.g.
-reduce current DMA mapping usage or delay and try again later).
+In some circumstances dma_map_single(), dma_map_page() and dma_map_resource()
+will fail to create a mapping. A driver can check for these errors by testing
+the returned DMA address with dma_mapping_error(). A non-zero return value
+means the mapping could not be created and the driver should take appropriate
+action (e.g.  reduce current DMA mapping usage or delay and try again later).

-- 
Regards,
Niklas Söderlund

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[PATCH v5 0/9] dmaengine: rcar-dmac: add iommu support for slave transfers Niklas Söderlund   <niklas.soderlund+renesas@ragnatech.se> - 2016-03-08 03:50 +0100
  [PATCH v5 4/9] arm: dma-mapping: add {map,unmap}_resource for iommu ops Niklas Söderlund   <niklas.soderlund+renesas@ragnatech.se> - 2016-03-08 03:50 +0100
  [PATCH v5 3/9] dma-mapping: add dma_{map,unmap}_resource Niklas Söderlund   <niklas.soderlund+renesas@ragnatech.se> - 2016-03-08 03:50 +0100
    Re: [PATCH v5 3/9] dma-mapping: add dma_{map,unmap}_resource Christoph Hellwig <hch@infradead.org> - 2016-03-08 08:40 +0100
      Re: [PATCH v5 3/9] dma-mapping: add dma_{map,unmap}_resource "Niklas S??derlund" <niklas.soderlund@ragnatech.se> - 2016-03-10 17:10 +0100
        Re: [PATCH v5 3/9] dma-mapping: add dma_{map,unmap}_resource Vinod Koul <vinod.koul@intel.com> - 2016-03-11 07:20 +0100
        Re: [PATCH v5 3/9] dma-mapping: add dma_{map,unmap}_resource Dan Williams <dan.j.williams@intel.com> - 2016-03-11 07:50 +0100
          Re: [PATCH v5 3/9] dma-mapping: add dma_{map,unmap}_resource Christoph Hellwig <hch@infradead.org> - 2016-03-11 12:20 +0100
            Re: [PATCH v5 3/9] dma-mapping: add dma_{map,unmap}_resource Niklas Söderlund   <niklas.soderlund@ragnatech.se> - 2016-03-11 14:00 +0100
              Re: [PATCH v5 3/9] dma-mapping: add dma_{map,unmap}_resource Christoph Hellwig <hch@infradead.org> - 2016-03-15 09:30 +0100
          Re: [PATCH v5 3/9] dma-mapping: add dma_{map,unmap}_resource Robin Murphy <robin.murphy@arm.com> - 2016-03-11 14:50 +0100
            Re: [PATCH v5 3/9] dma-mapping: add dma_{map,unmap}_resource Dan Williams <dan.j.williams@intel.com> - 2016-03-11 19:00 +0100
  [PATCH v5 9/9] ARM: dts: r8a7791: add iommus to dmac0 and dmac1 Niklas Söderlund   <niklas.soderlund+renesas@ragnatech.se> - 2016-03-08 03:50 +0100
  [PATCH v5 1/9] iommu: Add MMIO mapping type Niklas Söderlund   <niklas.soderlund+renesas@ragnatech.se> - 2016-03-08 03:50 +0100
  [PATCH v5 6/9] dmaengine: rcar-dmac: group slave configuration Niklas Söderlund   <niklas.soderlund+renesas@ragnatech.se> - 2016-03-08 03:50 +0100

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