Re: [PATCH v6 09/25] iommu: Allow an IDENTITY domain as the default_domain in ARM32

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On 2023/8/3 8:07, Jason Gunthorpe wrote:
Even though dma-iommu.c and CONFIG_ARM_DMA_USE_IOMMU do approximately the
same stuff, the way they relate to the IOMMU core is quiet different.

dma-iommu.c expects the core code to setup an UNMANAGED domain (of type
IOMMU_DOMAIN_DMA) and then configures itself to use that domain. This
becomes the default_domain for the group.

ARM_DMA_USE_IOMMU does not use the default_domain, instead it directly
allocates an UNMANAGED domain and operates it just like an external
driver. In this case group->default_domain is NULL.

If the driver provides a global static identity_domain then automatically
use it as the default_domain when in ARM_DMA_USE_IOMMU mode.

This allows drivers that implemented default_domain == NULL as an IDENTITY
translation to trivially get a properly labeled non-NULL default_domain on
ARM32 configs.

With this arrangment when ARM_DMA_USE_IOMMU wants to disconnect from the
device the normal detach_domain flow will restore the IDENTITY domain as
the default domain. Overall this makes attach_dev() of the IDENTITY domain
called in the same places as detach_dev().

This effectively migrates these drivers to default_domain mode. For
drivers that support ARM64 they will gain support for the IDENTITY
translation mode for the dma_api and behave in a uniform way.

Drivers use this by setting ops->identity_domain to a static singleton
iommu_domain that implements the identity attach. If the core detects
ARM_DMA_USE_IOMMU mode then it automatically attaches the IDENTITY domain
during probe.

Drivers can continue to prevent the use of DMA translation by returning
IOMMU_DOMAIN_IDENTITY from def_domain_type, this will completely prevent
IOMMU_DMA from running but will not impact ARM_DMA_USE_IOMMU.

This allows removing the set_platform_dma_ops() from every remaining
driver.

Remove the set_platform_dma_ops from rockchip and mkt_v1 as all it does
is set an existing global static identity domain. mkt_v1 does not support
IOMMU_DOMAIN_DMA and it does not compile on ARM64 so this transformation
is safe.

Tested-by: Steven Price<steven.price@xxxxxxx>
Tested-by: Marek Szyprowski<m.szyprowski@xxxxxxxxxxx>
Tested-by: Nicolin Chen<nicolinc@xxxxxxxxxx>
Signed-off-by: Jason Gunthorpe<jgg@xxxxxxxxxx>
---
  drivers/iommu/iommu.c          | 26 +++++++++++++++++++++++---
  drivers/iommu/mtk_iommu_v1.c   | 12 ------------
  drivers/iommu/rockchip-iommu.c | 10 ----------
  3 files changed, 23 insertions(+), 25 deletions(-)

Reviewed-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>

Best regards,
baolu



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