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SubjectRe: [BUILD FAILURE 01/04] Next June 04:PPC64 randconfig [drivers/staging/comedi/drivers.o]
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On Tue, 2009-06-09 at 13:50 +1000, Benjamin Herrenschmidt wrote:
> 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.

Ok. But, i am not sure whether Greg will agree to this. If, Ok, is the
following patch i sent earlier Ok ?

http://lkml.org/lkml/2009/6/5/462,

Regards--
Subrata

>
> 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.
>
> Cheers,
> Ben.
>
>
>
>



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