[PATCHv8 0/6] dmaengine: rcar-dmac: add iommu support for slave transfers

[Niklas Söderlund]

Hi,

This series tries to solve the problem with DMA with device registers
(MMIO registers) that are behind an IOMMU for the rcar-dmac driver. A
recent patch '9575632 (dmaengine: make slave address physical)'
clarifies that DMA slave address provided by clients is the physical
address. This puts the task of mapping the DMA slave address from a
phys_addr_t to a dma_addr_t on the DMA engine.

Without an IOMMU this is easy since the phys_addr_t and dma_addr_t are
the same and no special care is needed. However if you have a IOMMU you
need to map the DMA slave phys_addr_t to a dma_addr_t using something
like this.

This series is based on top of v4.7-rc1. And I'm hoping to be able to collect a 
Ack from Russell King on patch 4/6 that adds the ARM specific part and then be 
able to take the whole series through the dmaengine tree. If this is not the 
best route I'm more then happy to do it another way.

It's tested on a Koelsch with CONFIG_IPMMU_VMSA and by enabling the
ipmmu_ds node in r8a7791.dtsi. I verified operation by interacting with
/dev/mmcblk1, i2c and the serial console which are devices behind the
iommu.

Furthermore I have audited to the best of my ability all call paths
involved to make sure that the dma_addr_t obtained from
dma_map_resource() to is not used in a way where it would be expected
for the mapping to be RAM (have a struct page). Many thanks to Christoph
Hellwig and Laurent Pinchart for there input in this effort.

  * drivers/dma/sh/rcar-dmac.c
    Once the phys_addr_t is mapped to a dma_addr_t using
    dma_map_resource() it is only used to check that the transferee do not
    cross 4GB boundaries and then only directly written to HW registers.

  * drivers/iommu/iommu.c
    - iommu_map()
      Check that it's align to min page size or return -EINVAL then calls
      domain->ops->map()

  * drivers/iommu/ipmmu-vmsa.c
    - ipmmu_map()
      No logic only calls domain->ops->map()

  * drivers/iommu/io-pgtable-arm.c
    - arm_lpae_map()
      No logic only calls __arm_lpae_map()
    - __arm_lpae_map()
      No logic only calls arm_lpae_init_pte()
    - arm_lpae_init_pte()
      Used to get a pte:
        pte |= pfn_to_iopte(paddr >> data->pg_shift, data);

  * drivers/iommu/io-pgtable-arm-v7s.c
    - arm_v7s_map()
      No logic only calls __arm_v7s_map()
    - __arm_v7s_map()
      No logic only calls arm_v7s_init_pte()
    - arm_v7s_init_pte
      Used to get a pte:
        pte |= paddr & ARM_V7S_LVL_MASK(lvl);

  * ARM dma-mapping
    - dma_unmap_*
      Only valid unmap is dma_unmap_resource() all others are an invalid
      use case.
    - dma_sync_single_*
      Invalid use case, memory that is mapped is device memory
    - dma_common_mmap() and dma_mmap_attrs()
      Invalid use case
    - dma_common_get_sgtable() and dma_get_sgtable_attrs()
      Invalid use case, only for dma_alloc_* allocated memory,
    - dma_mapping_error()
      OK

* Changes since v7
- Use size_t instead of int for length in arm_iommu_map_resource() and 
  arm_iommu_unmap_resource().
- Fix bug in arm_iommu_map_resource() where wrong variable where passed to 
  __alloc_iova(). Thanks to Russell King for pointing out both errors.

* Changes since v6
- Use offset_in_page() and __pfn_to_phys(). This fixed a bug in the
  lib/dma-debug.c. Thanks to Konrad Rzeszutek Wilk for finding it and Robin
  Murphy for suggesting offset_in_page().
- Rebased on top of v4.7-rc1.
- Dropped DT patches which enabled the IPMMU on Renesas Koelsch and Lager. Will
  post them separately at a later time.

* Changes since v5
- Add dma-debug work which adds a new mapping type for the resource
  mapping which correctly can be translated to a physical address.
- Drop patches from Robin Murphy since they now are accepted in the
  iommu repository and base the series on that tree instead.
- Add a review tag from Laurent.

* Changes since v4
- Move the mapping from phys_addr_t to dma_addr_t from slave_config to the
  prepare calls. This way we know the direction of the mapping and don't have
  to use DMA_BIDIRECTIONAL. Thanks Vinod for suggesting this.
- To be clear that the data type for slave addresses are changed add a patch
  that only changes the data type to phys_addr_t.
- Fixed up commit messages.

* Changes since v3
- Folded in a fix from Robin to his patch.
- Added a check to make sure dma_map_resource can not be used to map RAM as
  pointed out by Robin. I use BUG_ON to enforce this. It might not be the best
  method but I saw no other good way since DMA_ERROR_CODE might not be defined
  on all platforms.
- Added comment about that DTS changes will disable 2 DMA channels due to a HW
  (?) bug in the DMAC.
- Dropped the use of dma_attrs, no longer needed.
- Collected Acked-by and Reviewed-by from Laurent.
- Various indentation fix ups.

* Changes since v2
- Drop patch to add dma_{map,unmap}_page_attrs.
- Add dma_{map,unmap}_resource to handle the mapping without involving a
  'struct page'. Thanks Laurent and Robin for pointing this out.
- Use size instead of address to keep track of if a mapping exist or not
  since addr == 0 is valid. Thanks Laurent.
- Pick up patch from Robin with Laurents ack (hope it's OK for me to
  attach the ack?) to add IOMMU_MMIO.
- Fix bug in rcar_dmac_device_config where the error check where
  inverted.
- Use DMA_BIDIRECTIONAL in rcar_dmac_device_config since we at that
  point can't be sure what direction the mapping is going to be used.

* Changes since v1
- Add and use a dma_{map,unmap}_page_attrs to be able to map the page
  using attributes DMA_ATTR_NO_KERNEL_MAPPING and
  DMA_ATTR_SKIP_CPU_SYNC. Thanks Laurent.
- Drop check if dmac is part of a iommu group or not, let the DMA
  mapping api handle it.
- Move slave configuration data around in rcar-dmac to avoid code
  duplication.
- Fix build issue reported by 'kbuild test robot' regarding phys_to_page
  not availability on some configurations.
- Add DT information for r8a7791.

* Changes since RFC
- Switch to use the dma-mapping api instead of using the iommu_map()
  directly. Turns out the dma-mapper is much smarter then me...
- Dropped the patch to expose domain->ops->pgsize_bitmap from within the
  iommu api.
- Dropped the patch showing how I tested the RFC.

Niklas Söderlund (6):
  dma-mapping: add {map,unmap}_resource to dma_map_ops
  dma-debug: add support for resource mappings
  dma-mapping: add dma_{map,unmap}_resource
  arm: dma-mapping: add {map,unmap}_resource for iommu ops
  dmaengine: rcar-dmac: group slave configuration
  dmaengine: rcar-dmac: add iommu support for slave transfers

 Documentation/DMA-API.txt   |  22 +++++++--
 arch/arm/mm/dma-mapping.c   |  63 ++++++++++++++++++++++++
 drivers/dma/sh/rcar-dmac.c  | 116 +++++++++++++++++++++++++++++++++++---------
 include/linux/dma-debug.h   |  19 ++++++++
 include/linux/dma-mapping.h |  42 ++++++++++++++++
 lib/dma-debug.c             |  52 +++++++++++++++++++-
 6 files changed, 285 insertions(+), 29 deletions(-)

-- 
2.8.2