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Subject[PATCH 0/8] Raspberry Pi 4 DMA addressing support
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 this discussion:

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 ARM cores, PCIe, V3D, GENET, and 40-bit DMA channels
have a wider view of the address space.

Part of this is solved in arm32 by setting up the machine specific
'.dma_zone_size = SZ_1G', which takes care of the allocating the
coherent memory area at the right spot. Yet 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 also
only ZONE_DMA32 is created which is interpreted by dma-direct and the
arm64 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:

- Add code that parses the device-tree in oder to find the SoC's common
DMA area.

- Create a ZONE_DMA whenever that area is needed and add the rest of the
lower 4 GB of memory to ZONE_DMA32*.

- Create the CMA area in a place suitable for all peripherals.

- Inform dma-direct of the new runtime calculated min_mask*.

That's all.


* These solutions where already discussed on the previous RFC (see link


Nicolas Saenz Julienne (8):
arm64: mm: use arm64_dma_phys_limit instead of calling
arm64: rename variables used to calculate ZONE_DMA32's size
of/fdt: add function to get the SoC wide DMA addressable memory size
arm64: re-introduce max_zone_dma_phys()
arm64: use ZONE_DMA on DMA addressing limited devices
dma-direct: turn ARCH_ZONE_DMA_BITS into a variable
arm64: update arch_zone_dma_bits to fine tune dma-direct min mask
mm: comment arm64's usage of 'enum zone_type'

arch/arm64/Kconfig | 4 ++
arch/arm64/mm/init.c | 78 ++++++++++++++++++++++++++-------
arch/powerpc/include/asm/page.h | 9 ----
arch/powerpc/mm/mem.c | 14 +++++-
arch/s390/include/asm/page.h | 2 -
arch/s390/mm/init.c | 1 +
drivers/of/fdt.c | 72 ++++++++++++++++++++++++++++++
include/linux/dma-direct.h | 2 +
include/linux/mmzone.h | 21 ++++-----
include/linux/of_fdt.h | 2 +
kernel/dma/direct.c | 8 ++--
11 files changed, 168 insertions(+), 45 deletions(-)


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