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SubjectRe: [BUILD FAILURE 01/04] Next June 04:PPC64 randconfig [drivers/staging/comedi/drivers.o]
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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