Hi Nicolas, Am 09.09.19 um 11:58 schrieb Nicolas Saenz Julienne: > 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 of these discussions: > v4: https://lkml.org/lkml/2019/9/6/352 > v3: https://lkml.org/lkml/2019/9/2/589 > v2: https://lkml.org/lkml/2019/8/20/767 > v1: https://lkml.org/lkml/2019/7/31/922 > RFC: https://lkml.org/lkml/2019/7/17/476 > > The new Raspberry Pi 4 has up to 4GB of memory but most peripherals can > only address the first GB: their DMA address range is > 0xc0000000-0xfc000000 which is aliased to the first GB of physical > memory 0x00000000-0x3c000000. Note that only some peripherals have these > limitations: the PCIe, V3D, GENET, and 40-bit DMA channels have a wider > view of the address space by virtue of being hooked up trough a second > interconnect. > > Part of this is solved on arm32 by setting up the machine specific > '.dma_zone_size = SZ_1G', which takes care of reserving the coherent > memory area at the right spot. That said no buffer bouncing (needed for > dma streaming) is available at the moment, but that's a story for > another series. > > Unfortunately there is no such thing as 'dma_zone_size' in arm64. Only > ZONE_DMA32 is created which is interpreted by dma-direct and the arm64 > arch code as if all peripherals where be able to address the first 4GB > of memory. > > In the light of this, the series implements the following changes: > > - Create both DMA zones in arm64, ZONE_DMA will contain the first 1G > area and ZONE_DMA32 the rest of the 32 bit addressable memory. So far > the RPi4 is the only arm64 device with such DMA addressing limitations > so this hardcoded solution was deemed preferable. > > - Properly set ARCH_ZONE_DMA_BITS. > > - Reserve the CMA area in a place suitable for all peripherals. > > This series has been tested on multiple devices both by checking the > zones setup matches the expectations and by double-checking physical > addresses on pages allocated on the three relevant areas GFP_DMA, > GFP_DMA32, GFP_KERNEL: > > - On an RPi4 with variations on the ram memory size. But also forcing > the situation where all three memory zones are nonempty by setting a 3G > ZONE_DMA32 ceiling on a 4G setup. Both with and without NUMA support. > i like to test this series on Raspberry Pi 4 and i have some questions to get arm64 running: Do you use U-Boot? Which tree? Are there any config.txt tweaks necessary?
