capture_mem limitations in OMAP ISP

Hi Laurent & co.,

I'm looking at the memory limitations in the omap3isp driver. 'struct isp_video' contains member 'capture_mem', which is set separately for each of our v4l2 video device nodes. The CCDC, for example, has capture_mem = 4096 * 4096 * 3 = 48MB, while the previewer and resizer each have twice that. Where do these numbers come from?

Is the CCDC incapable of DMA'ing more than 48MB into memory? I know that ISP_VIDEO_MAX_BUFFERS also limits the # of buffers, but I assume this is basically an arbitrary number so we can have a finite array of isp_video_buffer's. The 48MB, on the other hand, looks like it might have a good reason.

thanks,
Michael

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Hi Michael,

That's mostly historical. When developing the driver for the N900 we set a limit to avoid putting too much pressure on the system memory, and 3x8MP buffers was considered to be enough.

We could raise the limit, remove it completely, or implement a policy mechanism to let a privileged userspace application specify limits. The later might be interesting as a core V4L2 mechanism.

Regards,

Laurent Pinchart