Re: [PATCH] Add OMAP2 camera driver

["Trilok Soni" <soni.trilok@xxxxxxxxx>]

Hi Sakari,

On Tue, Dec 9, 2008 at 2:23 PM, Sakari Ailus <sakari.ailus@xxxxxxxxx> wrote:
> The DMA part is definitely the ugliest part of omap24xxcam.
>
> This is actually also a DMA controller driver. The system DMA driver could
> not be used as such as it was limited to just one controller --- the OMAP 2
> camera block has its own DMA controller with four transfers in queue
> (maximum).
>
> There's also an MMU, not the system MMU but the camera block MMU. This MMU
> is not being used now by omap24xxcam at all since when omap24xxcam driver
> was written, there was not too much time available and no generic MMU
> framework. So the MMU support was left out. Instead, there's a hack to
> allocate as large as possible continuous memory areas and avoid overruns
> that way. DMA transfer overruns happen on large proportion of frames without
> this hack.

This is due to legacy and carried forward to every new kernel version
from year 2004. I hope someone having H4 EVM can do it lot faster than
me, as I only have N8xx tablets, and debugging on them might be slow.

>
> Hiroshi Doyu is working on a generic IOMMU framework for OMAPs that could be
> used here. With that framework available, converting the OMAP 2 camera
> driver to use videobuf would be a lot easier. The performance would be
> better, too. A generic DMA controller driver would be also good to have but
> not mandatory.

This is not yet mainlined, so let's incorporate IOMMU bits once it
gets mainlined.


-- 
---Trilok Soni
http://triloksoni.wordpress.com
http://www.linkedin.com/in/triloksoni

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