On 17 December 2010 10:26, Saravana Kannan <skannan@xxxxxxxxxxxxxx> wrote: >>> Looks like you agree with our approach. If that's the case, would you >>> mind >>> Acking Jeff's initial patch that this thread is based on? >> >> I read Catalin's reply as agreeing with me. > > Catalin, Can you clarify? I'll try but I started my holidays and I'll only be online occasionally. Just to clarify, even if I ack Jeff's patch, it is for Russell to decide what gets merged. Now, Jeff's patch doesn't show anything about how the dma_alloc_coherent is used, just suggests something in the commit log, so I don't see it critical to this discussion. I wouldn't ack it without agreement on the extension of the DMA API (which can only have a no-op get_dma_ops at this point). I agree with Russell's points that just using the DMA API as it is may break in the future, hence a proposal to treat it slightly different. People in ARM working on a generic state save/restore mechanism face the same problem - they need some non-cacheable memory for synchronisation. I'm not sure whether they managed to find an alternative algorithm with cached memory and cache flushing and I also haven't followed the development to give more details. > Russell, > > I agree with your point about using an API for purpose and not property. > But I read Catalin's proposal as, let's treat secure domain as another DMA > "device". If we make a conscious agreement to do that, then using the DMA > API for secure domain would be "using it for its purpose" and we will make > an effort to not break it with future updates. Of course, if we don't > agree on that proposal, then we can't use the DMA API for secure domain > stuff. If there is no better proposal, I'm for such extension to the DMA API. >From the kernel perspecitve, the secure side is just another entity that accesses the RAM directly. It's not a physically separate device indeed but from a direct memory access perspective it can be treated as any other device. In the DMA API we can fall back to the non-coherent ops when a NULL struct device is passed. I assume in your code you already pass a NULL device to dma_alloc_coherent(). -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
