On Wednesday 29 July 2009 05:55:51 Mauro Carvalho Chehab wrote: > Em Wed, 29 Jul 2009 12:30:19 +0900 > > "Dongsoo, Nathaniel Kim" <dongsoo.kim@xxxxxxxxx> escreveu: > > Sorry my bad. I missed something very important to explain my issue > > clear. The thing is, I want to reserve specific amount of continuous > > physical memory on machine initializing time. Therefor some multimedia > > peripherals can be using this memory area exclusively. > > That's what I was afraid of could not being adopted in main line kernel. > > In the past, some drivers used to do that, but this is also a source > of problems, especially with general-purpose machines, where you're loosing > memory that could otherwise be used by something else. I never tried to get > the details, but I think the strategy were to pass a parameter during > kernel boot, for it to reserve some amount of memory that would later be > claimed by the V4L device. It's actually a pretty common strategy for embedded hardware (the "general- purpose machine" case doesn't - for now - make much sense on an OMAP processor for instance). A memory chunk would be reserved at boot time at the end of the physical memory by passing the mem= parameter to the kernel. Video applications would then mmap() /dev/mem to access that memory (I'd have to check the details on that one, that's from my memory), and pass the pointer the the v4l2 driver using userptr I/O. This requires root privileges, and people usually don't care about that when the final application is a camera (usually embedded in some device like a media player, an IP camera, ...). Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
