[BUILD FAILURE 01/04] Next June 04:PPC64 randconfig [drivers/staging/comedi/drivers.o]
benh at kernel.crashing.org
Tue Jun 9 13:50:18 EST 2009
On Sun, 2009-06-07 at 20:06 +0530, Subrata Modak wrote:
> On Sat, 2009-06-06 at 09:36 -0400, Frank Mori Hess wrote:
> > 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.
> Great to hear that. How about a patch that solves my build problem on
> PPC64(the problem seems to be existing for long) ?
In any case, doing PAGE_KERNEL_NOCACHE for DMA memory is incorrect on
many architectures. So at this stage, there's no much option but ifdef I
suspect for now until this is fixed properly.
It does make sense to want to have some memory like that shared between
user space and DMA, though I don't know what the right approach that
works on all archs is at this stage. Worth asking the Alsa guys, I think
they have similar issues :-)
But doing double buffering might do the trick fine for now.
More information about the Linuxppc-dev