[PATCH RFCv1] Support for zerocopy to DSP on OMAP3

[Arnout Vandecappelle <arnout@mind.be>]

 Here's a first attempt at allowing IO memory for USERPTR buffers.

 It also fixes another issue: it was assumed that 
dma->sglen == dma->nr_pages.  I'll split that up in a separate patch in the 
final version.

 Regards,
 Arnout

On Wednesday 03 March 2010 15:12:44, Arnout Vandecappelle wrote:
>  Hoi,
> 
>  [Please CC me, I'm not subscribed.]
> 
>  I'm implementing zerocopy transfer from a v4l2 camera to the DSP on an
> OMAP3 (based on earlier work by Stefan Kost [1][2]).  Therefore I'm using
> V4L2_MEMORY_USERPTR to pass in the memory area allocated by TI's DMAI
> driver.  However, this has flags VM_IO | VM_PFNMAP.  This means that it
> is not possible to do get_user_pages() on it - it's an area that is not
> pageable and possibly even doesn't pass the MMU.
> 
>  In order to support this kind of zerocopy construct, I propose to add
> checks for VM_IO | VM_PFNMAP and only get pages from areas that don't
> have these flags set.
> 
>  If I get positive feedback on this, I'll supply a patch.
> 
> 
> [1] https://bugzilla.gnome.org/show_bug.cgi?id=583890
> [2] http://thread.gmane.org/gmane.linux.drivers.video-input-
> infrastructure/6209

-- 
Arnout Vandecappelle                               arnout at mind be
Senior Embedded Software Architect                 +32-16-286540
Essensium/Mind                                     http://www.mind.be
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