On Monday, March 21, 2011 17:49:24 Guennadi Liakhovetski wrote:
> Hi Christian
>
> On Thu, 24 Feb 2011, Christian Gmeiner wrote:
>
> > Hi all,
> >
> > I jumped into the cold water and I am trying to convert the
> > dxr3/em8300 driver to the v4l2 api. I got some parts already working,
> > but I think
> > that the hardest parts are still missing. As you might think... yes I
> > have some questions :)
> >
> > 1) The dxr3 has a hardware fifo, which is used to play content. Can I
> > reuse videbuf1 or videbuf2 to manage the fifo? Are these
> > the frameworks designed to support output devices - write operation to
> > the device?
>
> Yes, videobuf* APIs are used for both input and output. I don't think you
> would be able to use videobuf1 for your set up, and you shouldn't anyway.
> As for videobuf2 - not sure... Are those hardware buffers purely internal
> to the hardware or can they also be directly accessed by the CPU as normal
> RAM? Even if it is possible in principle, using videobuf2, you would,
> probably, have to write your own memory-allocator. I'm sure others on this
> list can give a more qualified answer to this question;-)
vb2 should definitely be a good fit for this. That said, be aware that it
is quite new, so if you run into problems don't hesitate to ask on the list
just in case we overlooked something.
Also useful to know is that work will need to be done on the decoding API.
The ivtv driver does decoding as well. However, it uses a DVB API for that
(include/linux/dvb/video.h and audio.h). In hindsight this was a bad idea
and instead a proper V4L2 API should be created. This can be based on the
those headers. I can help with that, time permitting.
Regards,
Hans
>
> > Here you can find the current fifo impl.
> > https://github.com/austriancoder/v4l2-em8300/blob/master/modules/em8300_fifo.c
> >
> > 2) The adv7175 chip support to different input data types:
> >
> > Video Input Data Port Supports:
> > CCIR-656 4:2:2 8-Bit Parallel Input Format
> > 4:2:2 16-Bit Parallel Input Format
> >
> > See http://dxr3.sourceforge.net/download/hardware/ADV7175A_6A.pdf for
> > more details about the chip.
> >
> > Now I thought that I should use the v4l2-mediabus api for that, but I
> > am not sure what pixel codes (V4L2_MBUS_FMT...)
> > should be used for CCIR-656 4:2:2 8-Bit and CCIR-656 4:2:2 16-Bit.
>
> Yes, you should use mediabus formats, and no, these formats are not
> defined yet. Please, propose a patch with these two new formats.
>
> Thanks
> Guennadi
> ---
> Guennadi Liakhovetski, Ph.D.
> Freelance Open-Source Software Developer
> http://www.open-technology.de/
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--
Hans Verkuil - video4linux developer - sponsored by Cisco
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