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

On Tue, Jun 9, 2009 at 20:34, Subrata Modak[off-list ref] wro=
te:

On Tue, 2009-06-09 at 13:50 +1000, Benjamin Herrenschmidt wrote:

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On Sun, 2009-06-07 at 20:06 +0530, Subrata Modak wrote:

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On Sat, 2009-06-06 at 09:36 -0400, Frank Mori Hess wrote:

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On Saturday 06 June 2009, Greg KH wrote:

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Frank and Ian, any thoughts about the vmap call in the
comedi_buf_alloc() call? =C2=A0Why is it using PAGE_KERNEL_NOCACHE=

, and what

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is the prealloc_buf buffer used for?

It is a circular buffer used to hold data streaming either to or fro=

m a

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board (for example when producing an analog output waveform). =C2=A0=

Reads and

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writes to the device files read/write to the circular buffer, plus a=

 few

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drivers do dma directly to/from it. =C2=A0I personally don't have a =

problem

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with requiring drivers to have their own dma buffers and making them=

 copy

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data between their private dma buffers and the main circular buffer.=

 =C2=A0I

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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,

Your patch helps powerpc only. Compilation is still broken on most
other architectures.

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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.

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k=
.org

In personal conversations with technical people, I call myself a hacker. Bu=
t
when I'm talking to journalists I just say "programmer" or something like t=
hat.
							    -- Linus Torvalds