[PATCH v6 0/4] Raspberry Pi 4 DMA addressing support
From: Nicolas Saenz Julienne
Date: Wed Sep 11 2019 - 14:25:57 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 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
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 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,
- 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 a Cavium ThunderX2 with 256GB 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 v6:
- Fix bug in max_zone_phys()
Changes in v5:
- Fix issue with swiotlb initialization
Changes in v4:
- Rebased to linux-next
- Fix issue when NUMA=n and ZONE_DMA=n
- Merge two max_zone_dma*_phys() functions
Changes in v3:
- Fixed ZONE_DMA's size to 1G
- Update mmzone.h's comment to match changes in arm64
- Remove all dma-direct patches
Changes in v2:
- Update comment to reflect new zones split
- ZONE_DMA will never be left empty
- Try another approach merging both ZONE_DMA comments into one
- Address Christoph's comments
- If this approach doesn't get much traction I'll just drop the patch
from the series as it's not really essential
Nicolas Saenz Julienne (4):
arm64: mm: use arm64_dma_phys_limit instead of calling
arm64: rename variables used to calculate ZONE_DMA32's size
arm64: use both ZONE_DMA and ZONE_DMA32
mm: refresh ZONE_DMA and ZONE_DMA32 comments in 'enum zone_type'
arch/arm64/Kconfig | 4 ++
arch/arm64/include/asm/page.h | 2 +
arch/arm64/mm/init.c | 71 +++++++++++++++++++++++++----------
include/linux/mmzone.h | 45 ++++++++++++----------
4 files changed, 83 insertions(+), 39 deletions(-)