Hi all, this series attempts to address some issues we found while bringing up the new Raspberry Pi 4 in arm64 and it's intended to serve as a follow up to this: https://www.spinics.net/lists/arm-kernel/msg740650.html
The new Raspberry Pi 4 has up to 4GB of ram but most devices can only address the first GB of ram: the DMA address range is 0xc0000000-0xfc000000 which is aliased to the first GB of memory 0x00000000-0x3c000000. Note that only some devices have this limitations, the ARM cores, PCIe, GENET, and 40-bit DMA channels have a wider view of the address space. This is solved in arm32 by setting up the correct '.dma_zone_size = SZ_1G' which takes care of the allocating the coherent memory area at the right spot and also is taken into account in the arch specific 'dma_map_ops'. Unfortunately there is no such thing as '.dma_zone_size' in arm64, to make things worse it's assumed that all devices will be able to adress the first 4GB of memory. This raises two issues: the coherent memory reserves are located in an area not accessible by most devices, and DMA streaming's dma_supported(), which fails for most devices since it's min_mask isn't properly set. Note that the rest if DMA streaming works fine thanks to the help of swiotlb. On one hand I've implemented a function that parses the 'dma-range' on all interconnects and tries to select a location for the coherent memory reserves that'll fit all devices. I made the algorithm as simple as possible, based on the existing devices limitations. On the other I've added a new variable in dma-direct that allows modifying the min_mask during the init process and taken care of setting it accordingly in the arm64's init code. Regards, Nicolas --- Nicolas Saenz Julienne (4): arm64: mm: use arm64_dma_phys_limit instead of calling max_zone_dma_phys() arm64: mm: parse dma-ranges in order to better estimate arm64_dma_phys_limit dma-direct: add dma_direct_min_mask arm64: mm: set direct_dma_min_mask according to dma-ranges arch/arm64/mm/init.c | 69 ++++++++++++++++++++++++++++++++++++++++---- kernel/dma/direct.c | 4 ++- 2 files changed, 67 insertions(+), 6 deletions(-) -- 2.22.0
