>-----Original Message----- >From: Arnd Bergmann [mailto:arnd@xxxxxxxx] >Sent: Thursday, September 11, 2014 6:45 PM >To: Lu Jingchang-B35083 >Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; Guo Shawn-R65073; >devicetree@xxxxxxxxxxxxxxx >Subject: Re: [PATCHv3 5/6] ARM: imx: Add initial support for Freescale >LS1021A > >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 I will do that. Thanks. Best Regards, Jingchang ��.n��������+%������w��{.n����z�{��ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f
