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? Rob -- 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
