On Tue, Jan 09, 2024 at 12:03:43PM +0200, Baruch Siach wrote: > On Mon, Jan 08 2024, Catalin Marinas wrote: > > On Wed, Dec 27, 2023 at 05:04:27PM +0200, Baruch Siach wrote: > >> Current code using zone_dma_bits assume that all addresses range in the > >> bits mask are suitable for DMA. For some existing platforms this > >> assumption is not correct. DMA range might have non zero lower limit. > >> > >> Add 'zone_dma_off' for platform code to set base address for DMA zone. > >> > >> Rename the dma_direct_supported() local 'min_mask' variable to better > >> describe its use as limit. > >> > >> Suggested-by: Catalin Marinas <catalin.marinas@xxxxxxx> > > > > When I suggested taking the DMA offsets into account, that's not exactly > > what I meant. Based on patch 4, it looks like zone_dma_off is equivalent > > to the lower CPU address. Let's say a system has DRAM starting at 2GB > > and all 32-bit DMA-capable devices has a DMA offset of 0. We want > > ZONE_DMA32 to end at 4GB rather than 6GB. > > Patch 4 sets zone_dma_off to the lower limit from 'dma-ranges' property > that determines zone_dma_bits. This is not necessarily equivalent to > start of DRAM, though it happens to be that way on my platform. A bit better but it still assumes that all devices have the same DMA offset which may not be the case. -- Catalin
