On Thu, Mar 10, 2016 at 05:05:23PM +0100, Niklas S??derlund wrote: > 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) Using function prototypes in documentation may not be a great idea as you are explaining the role of this function and not arguments. > + > +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 -- ~Vinod
