On Monday 21 April 2014 11:35 AM, Rob Herring wrote: > On Mon, Apr 21, 2014 at 10:13 AM, Santosh Shilimkar > <santosh.shilimkar@xxxxxx> wrote: >> Hi Rob, >> >> On Monday 21 April 2014 10:37 AM, Rob Herring wrote: >>> On Sat, Apr 19, 2014 at 9:32 AM, Santosh Shilimkar >>> <santosh.shilimkar@xxxxxx> 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. >>> >>> Can you briefly describe what the h/w looks like in terms of addresses >>> for the problem you are trying to solve? Something like: Cpu view of >>> RAM is X to Y address, X corresponds to DMA address Z. Max DMA address >>> is ? >>> >> Let me try with say 8 GB RAM example >> >> CPU view of memory : 0x0000 0008 0000 0000 to 0x0000 000a 0000 0000 >> >> From above memory range, first 2 GB of memory has an alias 32 bit >> view in the hardware. Hardware internally map the address issued within >> that first 2 GB to same memory. >> >> DMA view of first 2 GB [ 0x0000 0008 0000 0000 to 0x0000 0008 7fff ffff] >> is : 0x8000 0000 to 0xffff fffff. > > Are you setting ZONE_DMA to be 2GB so allocations stay within DMAable > memory and that is enough that you don't need to set DMA masks? > Yes. Thats right. Regards, Santosh -- 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
