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From: Patrick =?ISO-8859-15?Q?Lamaizi=E8re?= <patfbsd@davenulle.org>
To: John Baldwin <jhb@freebsd.org>
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Cc: freebsd-hackers@freebsd.org
Subject: Re: problem with bus_dmamap_load_uio
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Le Mon, 3 Nov 2008 18:49:57 -0500,
John Baldwin <jhb@freebsd.org> a écrit :

Hello,

> > I don't understand why bus_dmamap_load_uio() cannot load the uio.
> > Also when it fails, i copy the uio into a buffer and then a
> > bus_dmamap_load() of the buffer always works.
> > 
> > The dma tag is allocated with:
> > 
> > bus_dma_tag_create(bus_get_dma_tag(sc->sc_dev),/* parent */
> >  16, 0,                   /* alignments, bounds */
> >  BUS_SPACE_MAXADDR_32BIT, /* lowaddr */
> >  BUS_SPACE_MAXADDR,       /* highaddr */
> >  NULL, NULL,              /* filter, filterarg */
> >  16384,                   /* maxsize */
> >  1,                       /* nsegments */
> >  16384,                   /* maxsegsize */
> >  BUS_DMA_ALLOCNOW,        /* flags */
> >  NULL, NULL,              /* lockfunc, lockarg */
> >  &sc->sc_dmat);

...

> Your dma tag only allows a single scatter/gather entry (nsegments).
> What is happening is that under memory pressure, the virtual buffer
> in userland is not built from physically contiguous pages, so you
> would need multiple s/g entries to describe the buffer.  Hence
> EFBIG.  

Thank you John, you save me!

> If your hardware can handle multiple s/g entries, then just
> increase 'nsegments' and handle the multiple segments in your
> callback routine.

Unfortunely it does not.

Regards.