On Wednesday 10 September 2014 03:31:19 Jingchang Lu wrote: > >> +DT_MACHINE_START(LS1021A, "Freescale LS1021A") > >> + #ifdef CONFIG_ZONE_DMA > >> + .dma_zone_size = SZ_128M, > >> +#endif > >> + .init_machine = ls1021a_init_machine, > >> + .dt_compat = ls1021a_dt_compat, > >> + .restart = mxc_restart, > >> +MACHINE_END > > > >I believe someone recently posted a patch to derive the dma_zone_size from > >device tree. Can yo try to find that and see if that will work for you? > > > >Can you explain what the reason is for needing a DMA zone? > > With LPAE enabled on our SoC, we meet the system complaint of > "coherent DMA mask 0xffffffff is smaller than system GFP_DMA mask 0xffffffffffffffff", > and I notice that CONFIG_ZONE_DMA and dma_zone_size is a common resolve for this. Ok, I see. The actual point of dma_zone_size however is slightly different, and I think you should not use it like this. We normally only use ZONE_DMA if there are devices that have a limitation smaller than 4GB, and that appear to be the case for your system. The message you quote is only present in arch/powerpc, so I'm not sure what symptoms you are actually seeing. Please try removing the dma_zone_size setting for your platform and report if it works or what the symptom is if it does not work with the latest kernel. We definitely need to get this to work out of the box without a dma_zone_size hack. Can you describe what the memory layout is of your platform? Can you have RAM installed above the 4GB physical address boundary? If you can, are there any devices that are unable to perform DMA into that memory without the use of an IOMMU? Arnd -- 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
