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

From: Frank Mori Hess <[email-masked]>
Date: Sat, 6 Jun 2009 09:36:17 -0400

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.