A handful of DMA topics
Posted Jul 1, 2004 12:49 UTC (Thu) by jamey
In reply to: A handful of DMA topics
Parent article: A handful of DMA topics
For the devices for which Ian and I are writing drivers, the CPU accesses the device's internal memory via the CPU memory bus. On other platforms, the CPU might access the internal memory via an IO bus. The new DMA calls proposed by James Bottomley (dma_declare_coherent_memory and dma_release_coherent_memory) handle either case.
Many drivers for such devices used ioremap and private memory allocators. What caused us to propose this change was the use of standard device hardware interfaces (UCB OHCI) in the context of a chip with direct access only to private SRAM. In the past, we made extensive modifications to drivers such as the USB OHCI driver to support these devices. However, it appeared that the 2.6 device model and the generic DMA API would enable us to clean this up and to produce drivers acceptable to the mainstream kernel.
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