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

Baolu Lu
2023-08-14T04:33:29Z

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@arm.com>
> Tested-by: Marek Szyprowski<m.szyprowski@samsung.com>
> Tested-by: Nicolin Chen<nicolinc@nvidia.com>
> Signed-off-by: Jason Gunthorpe<jgg@nvidia.com>
> ---
> 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@linux.intel.com>

Best regards,
baolu