Messages in this thread | | | From | David Laight <> | Subject | RE: [PATCH 3/3] dma-mapping: better document dma_addr_t and DMA_MAPPING_ERROR | Date | Tue, 22 Sep 2020 13:56:46 +0000 |
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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
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