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). 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. 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?). 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? Thanks, Thomas -- Thomas Petazzoni, CTO, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com -- 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
