From: Christoph Hellwig > Sent: 22 September 2020 14:40 ... > @@ -131,6 +125,16 @@ struct dma_map_ops { > unsigned long (*get_merge_boundary)(struct device *dev); > }; > > +/* > + * A dma_addr_t can hold any valid DMA or bus address for the platform. It > can > + * be given to a device to use as a DMA source or target. A CPU cannot > + * reference a dma_addr_t directly because there may be translation between > its > + * physical address space and the bus address space.
It can't access it 'directly' because it isn't a virtual address.... > + * > + * DMA_MAPPING_ERROR is the magic error code if a mapping failed. It should > not > + * be used directly in drivers, but checked for using dma_mapping_error() > + * instead. > + */ I think it might be worth adding: A dma_addr_t value may be device dependant and differ from the 'physical address' of the memory. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu