>-----Original Message----- >From: Arnd Bergmann [mailto:arnd@xxxxxxxx] >Sent: Wednesday, September 10, 2014 3:42 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 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 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. 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. Best Regards, Jingchang ��.n��������+%������w��{.n����z�{��ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f
