[PATCH v2 00/11] Raspberry Pi 4 DMA addressing support
From: Nicolas Saenz Julienne
Date: Tue Aug 20 2019 - 10:58:35 EST
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:
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
Part of this is solved in 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
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
In the light of this, the series implements the following changes:
- Create generic 'dma_zone_size' in order for hardware description code
to set it up when needed.
- Add a function in early_init_dt_scan() to setup 'dma_zone_size' for
- Create both DMA zones in arm64, ZONE_DMA will contain the area
addressable by all peripherals and ZONE_DMA32 the rest of the 32 bit
addressable memory. ZONE_DMA32 might be left empty.
- Reserve the CMA area in a place suitable for all peripherals.
- Inform dma-direct of the new runtime calculated min_mask.
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,
- 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.
- On a Synquacer box with 32G of memory.
- On an ACPI based Huawei TaiShan server with 256G of memory.
- On a QEMU virtual machine running arm64's OpenSUSE Tumbleweed.
Changes in v2:
- More in depth testing.
- Create new global 'dma_zone_size'.
- New approach to getting the dma_zone_size, instead of parsing the dts
we hardcode it conditionally to the machine compatible name.
- Fix ZONE_DMA and ZONE_DMA32 split, now ZONE_DMA32 remains empty if
ZONE_DMA fits the whole 32 bit addressable space.
- Take into account devices with DMA offset.
- Rename new dma-direct variable to zone_dma_bits.
- Try new approach by merging both ZONE_DMA and ZONE_DMA32 comments
in mmzone.h, add new up to date examples.
Nicolas Saenz Julienne (11):
asm-generic: add dma_zone_size
arm: use generic dma_zone_size
of/fdt: add of_fdt_machine_is_compatible function
of/fdt: add early_init_dt_get_dma_zone_size()
arm64: mm: use arm64_dma_phys_limit instead of calling
arm64: rename variables used to calculate ZONE_DMA32's size
arm64: re-introduce max_zone_dma_phys()
arm64: use both ZONE_DMA and ZONE_DMA32
dma-direct: turn ARCH_ZONE_DMA_BITS into a variable
arm64: edit zone_dma_bits to fine tune dma-direct min mask
mm: refresh ZONE_DMA and ZONE_DMA32 comments in 'enum zone_type'
arch/arm/include/asm/dma.h | 8 ++--
arch/arm/mm/init.c | 12 ++----
arch/arm64/Kconfig | 4 ++
arch/arm64/mm/init.c | 73 +++++++++++++++++++++++++--------
arch/powerpc/include/asm/page.h | 9 ----
arch/powerpc/mm/mem.c | 16 +++++---
arch/s390/include/asm/page.h | 2 -
arch/s390/mm/init.c | 1 +
drivers/of/fdt.c | 15 +++++++
include/asm-generic/dma.h | 8 +++-
include/linux/dma-direct.h | 2 +
include/linux/mmzone.h | 46 ++++++++++++---------
kernel/dma/direct.c | 13 +++---
mm/page_alloc.c | 3 ++
14 files changed, 140 insertions(+), 72 deletions(-)