On Thursday 11 September 2014 09:53:56 Jingchang Lu wrote: > >From: Arnd Bergmann [mailto:arnd@xxxxxxxx] > > > >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? > > > Our first LS1021A support is based on kernel-3.12, where when LPAE enabled > it will compare the device's coherent_dma_mask with arm_dma_limit, which is > 64-bit 0xffffffffffffffff without CONFIG_ZONE_DMA, with CONFIG_ZONE_DMA can > limit the comparison and avoid the warning. > All device can address 32-bit address space on LS1021A, With you comment above, > I remove the dma_zone_size and only reserve the CONFIG_ZONE_DMA On kernel-3.12, > finding all works well, so I will remove the dma_zone_size setting on 3.12. Thanks. Ok, good. > I have a look on latest kernel, finding get_coherent_dma_mask() has limited the mask > to (u64)DMA_BIT_MASK(32), does this mean the CONFIG_ZONE_DMA is not needed for me > here? Thanks. You only need to enable CONFIG_ZONE_DMA in the case of RAM above the 4GB boundary. I would suggest you do the same as some of the other platforms by adding select ZONE_DMA if ARM_LPAE into your Kconfig file. If LPAE is disabled, you know that you won't need ZONE_DMA. 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
