On Saturday 06 June 2009, Greg KH wrote: > Frank and Ian, any thoughts about the vmap call in the > comedi_buf_alloc() call? Why is it using PAGE_KERNEL_NOCACHE, and what > is the prealloc_buf buffer used for?
It is a circular buffer used to hold data streaming either to or from a board (for example when producing an analog output waveform). Reads and writes to the device files read/write to the circular buffer, plus a few drivers do dma directly to/from it. I personally don't have a problem with requiring drivers to have their own dma buffers and making them copy data between their private dma buffers and the main circular buffer. I guess the original design wanted to support zero-copy dma.
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