[PATCHv2 3/9] v4l: add buffer exporting via dmabuf

[Rémi Denis-Courmont]

Le mardi 31 juillet 2012 19:28:12 Laurent Pinchart, vous avez écrit :
> Hi Rémi,
> 
> On Tuesday 31 July 2012 16:39:00 Rémi Denis-Courmont wrote:
> > Le mardi 31 juillet 2012 14:56:14 Laurent Pinchart, vous avez écrit :
> > > > For that matter, wouldn't it be useful to support exporting a userptr
> > > > buffer at some point in the future?
> > > 
> > > Shouldn't USERPTR usage be discouraged once we get dma-buf support ?
> > 
> > USERPTR, where available, is currently the only way to perform zero-copy
> > from kernel to userspace. READWRITE does not support zero-copy at all.
> > MMAP only supports zero-copy if userspace knows a boundary on the number
> > of concurrent buffers *and* the device can deal with that number of
> > buffers; in general, MMAP requires memory copying.
> 
> Could you please share your use case(s) with us ?

I want to receive the video buffers in user space for processing. Typically 
"processing" is software encoding or conversion. That's what virtually any V4L 
application does on the desktop...

-- 
Rémi Denis-Courmont
http://www.remlab.net/
http://fi.linkedin.com/in/remidenis