On Saturday 19 April 2014 12:25 PM, Thomas Petazzoni wrote: > Dear Santosh Shilimkar, > > On Sat, 19 Apr 2014 10:32:45 -0400, Santosh Shilimkar wrote: >> Here is an updated version of [2] based on discussion. Series introduces >> support for setting up dma parameters based on device tree properties >> like 'dma-ranges' and 'dma-coherent' and also update to ARM 32 bit port. >> Earlier version of the same series is here [1]. >> >> The 'dma-ranges' helps to take care of few DMAable system memory restrictions >> by use of dma_pfn_offset which we maintain now per device. Arch code then >> uses it for dma address translations for such cases. We update the >> dma_pfn_offset accordingly during DT the device creation process.The >> 'dma-coherent' property is used to setup arch's coherent dma_ops. >> >> After some off-list discussion with RMK and Arnd, I have now dropped the >> controversial dma_mask setup code from the series which actually isn't blocking >> me as such. Considering rest of the parts of the series are already aligned, >> am hoping to get this version merged for 3.16 merge window. >> >> We agreed in last discussion that drivers have the ultimate >> responsibility to setup the correct dma mask but then we need to have some >> means to see if bus can support what driver has requested for a case where >> driver request for bigger mask than what bus supports. I can follow up on >> the mask topic if we have broken drivers. > > I am not sure whether there is an intersection or not, but I wanted to > mention that the mvebu platform (in mach-mvebu) supports hardware I/O > coherency, which makes it a coherent DMA platform. However, we are not > able to use arm_coherent_dma_ops for this platform, because when a > transfer is being made DMA_FROM_DEVICE, at the end of the transfer, we > need to perform an I/O barrier to wait for the snooping unit to > complete its coherency work. So we're coherent, but not with > arm_coherent_dma_ops: we have our own dma operation implementation (see > arch/arm/mach-mvebu/coherency.c). > I have seen that. > However, it seems that your patch series, at least in PATCH 6/7 makes > the assumption that for all DMA coherent platforms, > arm_coherent_dma_ops is going to be OK. > No it doesn't. The infrastructure is for all the common cases which can just use arm generic dma_ops. > Also, I haven't followed all the discussions, but what is the intended > usage of of_dma_is_coherent() and set_arch_dma_coherent_ops() (device > drivers? platform code?). > The intention is for sub arch's like ARM, ARM64, powerPC etc can set the dma_ops based on the device tree property. Today the ARM coherent machines are doing that in machine code and we want to move that to more generic code. > In mach-mvebu, what we do is that we register a bus notifier on the > platform bus, so that we can set our custom DMA operations for all > platform devices in the system. Should this be done in a different way > after your series? > Nope. Since you have a very custom SOC specific case, you can continue what you are doing. Regards, Santosh -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
