Hi Laurent, You make this very clear, thank you! The ISP on Medfield do have its own IOMMU. And I also think an IOMMU layer for ISP is needed. I'm not quite understand "unless hardware design doesn't give you a choice about that,". Can you explain more on that? Also regarding to the VCMM (Virtual Contiguous Memory Manager) or CMA, is it also an option? Thanks Wen >-----Original Message----- >From: Laurent Pinchart [mailto:laurent.pinchart@xxxxxxxxxxxxxxxx] >Sent: 2011年2月10日 17:29 >To: Gao, Bin >Cc: Wang, Wen W; Kanigeri, Hari K; Iyer, Sundar; Yang, Jianwei; >linux-media@xxxxxxxxxxxxxxx; umg-meego-handset-kernel@xxxxxxxxxxxxxxxxxxxxxxx; >Jozef Kruger >Subject: Re: Memory allocation in Video4Linux > >Hi Wen, > >On Thursday 10 February 2011 08:59:38 Gao, Bin wrote: >> Penwell has IOMMU feature? >> As far as I know only part of Intel server processors have this feature >> which is designed originally for VT(virtualization technology). >> >> Wen, >> Can you refer to other ISP Soc drivers and see how they are dealing with >> this issue? I don't understand why you need to manage MMU inside ISP, I >> think the real problem is how can we allocate a large number of memory >> pages from IA side where ISP can access to by DMA. Any ISP document can be >> shared to help us understand what's the problem? > >I second this request. It's not totally clear to me from this mail thread >whether your ISP has its own MMU (which would then be considered as an IOMMU), >or accesses the system memory through other means (continuous buffers, >scatter-gather lists, ...). > >If the Medfield ISP includes an IOMMU, the IOMMU layer is probably what you >want to use. Memory can then be allocated using a simple vmalloc(), and pages >can be mapped to the ISP memory space using the IOMMU. > >Please note that, unless the ISP IOMMU is already supported by the Linux >kernel, you will obviously need to implement an IOMMU driver for it. What you >shouldn't do is put that code in the ISP driver (unless hardware design >doesn't give you a choice about that, but I need to see more documentation to >answer this question). > >-- >Regards, > >Laurent Pinchart ?韬{.n?????%??檩??w?{.n???{炳g???^n?■???h?璀?｛?夸z罐?+€?zf＂?????i?????_璁?:+v??撸?
