[PATCH v6 0/2] dma: support DMA zone starting above 4GB

[Baruch Siach]

From: Baruch Siach <baruchs-c@xxxxxxxxxxxxx>

DMA zones code assumes that DMA lower limit is zero. When there is no RAM 
below 4GB, arm64 platform code sets DMA/DMA32 zone limits to cover the entire 
RAM[0].

My target platform has RAM starting at 32GB. Devices with 30-bit DMA mask are 
mapped to 1GB at the bottom of RAM, between 32GB - 33GB. DMA zone over the 
entire RAM breaks DMA allocation for these devices.

In response to a previous RFC hack[1] Catalin Marinas suggested to add a
separate offset value as base address for the DMA zone, and then refined the 
suggestion to use start of RAM[3]. This series attempts to implement that 
suggestion.

With this series applied, the DMA zone covers the right RAM range for my 
platform.

v6:

  * Drop the first patch; existing logic is just fine

  * Modify powerpc code to avoid off by one issue

v5:

  * Test the correct kernel

  * Add missing patch that actually makes DMA zone work

  * Extend the treatment of zone_dma_limit > DMA_BIT_MASK(32)

  * Use max() to make the code somewhat more readable

  * Change zone_dma_limit type to u64 to match DMA_BIT_MASK()

v4:

  * Drop last patch. zone_dma_limit includes RAM base address.

  * Adjust DMA zone selection in swiotlb as well.

  * Don't change max_zone_phys() behaviour

  * Update code to fallback to DMA zone when zone_dma_limit > DMA_BIT_MASK(32)

v3:

  * Rebase on v6.11-rc1.

  * Drop zone_dma_base. Use memblock_start_of_DRAM() instead.

  * Drop DT patches. Low DMA range limit no longer needed.

  * Add patch to improve dma_direct_optimal_gfp_mask() heuristics as Catalin 
    suggested.

RFC v2:

  * Add patch from Catalin[2] changing zone_dma_bits to zone_dma_limit to 
    simplify subsequent patches

  * Test on real hardware

RFC v1: https://lore.kernel.org/all/cover.1703683642.git.baruch@xxxxxxxxxx/

[0] See commit 791ab8b2e3db ("arm64: Ignore any DMA offsets in the 
    max_zone_phys() calculation")

[1] https://lore.kernel.org/all/9af8a19c3398e7dc09cfc1fbafed98d795d9f83e.1699464622.git.baruch@xxxxxxxxxx/

[2] https://lore.kernel.org/all/ZZ2HnHJV3gdzu1Aj@xxxxxxx/

[3] https://lore.kernel.org/all/ZnH-VU2iz9Q2KLbr@xxxxxxx/

Catalin Marinas (2):
  dma: replace zone_dma_bits by zone_dma_limit
  arm64: support DMA zone above 4GB

 arch/arm64/mm/init.c       | 32 ++++++++++----------------------
 arch/powerpc/mm/mem.c      |  5 ++++-
 arch/s390/mm/init.c        |  2 +-
 include/linux/dma-direct.h |  2 +-
 kernel/dma/direct.c        |  6 +++---
 kernel/dma/pool.c          |  4 ++--
 kernel/dma/swiotlb.c       |  6 +++---
 7 files changed, 24 insertions(+), 33 deletions(-)


base-commit: 8400291e289ee6b2bf9779ff1c83a291501f017b
-- 
2.43.0