>-----Original Message----- >From: Laurent Pinchart [mailto:laurent.pinchart@xxxxxxxxx] >Sent: Wednesday, July 29, 2009 3:06 PM >To: Karicheri, Muralidharan >Cc: Mauro Carvalho Chehab; Dongsoo, Nathaniel Kim; v4l2_linux; Dongsoo Kim; >박경민; jm105.lee@xxxxxxxxxxx; 이세문; 대인기; 김형준 >Subject: Re: How to save number of times using memcpy? > >On Wednesday 29 July 2009 20:36:25 Karicheri, Muralidharan wrote: >> <Snip> >> >> > > 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, ...). >> >> Yes. This is exactly what we are doing in the case of davinci processors. >> We have a kernel module that uses memory from the end of SDRAM space and >> mmap it to application through a set of APIs. They allocate contiguous >> memory pools and return the same to application through IOCTLs. I have >> tested vpfe capture using this approach (but yet to push the same to v4l2 >> community for review). The same approach may be used across other >platforms >> as well. So doesn't it make sense to add this kernel module to the kernel >> tree so that everyone can use it? > >What's wrong with mmap()'ing /dev/mem ? Why do you need a special driver ? > Could you please explain this? I am not sure what your suggestion is. >Regards, > >Laurent Pinchart > 淸{.n+돴윯돪+%듚깁負w{.n+돴{깸g돬왲^nr⊆z곷h솳鈺&｛z요z받쀺++zf＂h닱~넮녬i곴묎z_溫j:+v돣)山m
