Re: Writing first v4l2 driver

[Jon Dufresne <jon.dufresne@infinitevideocorporation.com>]

On Thu, 2008-06-05 at 18:07 -0300, Mauro Carvalho Chehab wrote:
> Does your device support DMA scatter/gather mode (e.g. instead of a continuous
> DMA memory, you would be using a range of non-continuous memory areas)? If not,
> then you'll need to write a different video-buf driver.

I am writing code for both sides, the DSP on the PCI board and the
driver in the linux kernel. The dsp has functionality to write data over
the PCI bus, and I could certainly code this to work in discontinuous
chunks. So I believe it could use sg lists.


> The simplest driver is vivi.c. Yet, it uses videobuf-vmalloc, which is a little
> bit different. However, since this is a fake device, it helps to understand how
> videobuf works. If you get into vivi.c previous versions, at mercurial repo,
> you'll find even a vivi example using the video-buf-dma-sg. Most of stuff
> will be similar. 
> 
> The other two examples for PCI devices are saa7134-video and cx88-video. bttv
> also uses it, but bttv driver is more complex to understand, since its code is
> bigger.

Thanks for pointing these devices out. I will study these and see how
things turn out.

Thanks again,
Jon

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