Dear All,
This is an initial RFC on the unification of IOMMU-based DMA-mapping code for ARM and ARM64 architectures.
Right now ARM architecture still use my old code for IOMMU-based DMA-mapping glue, initially merged in commit 4ce63fcd919c32d22528e54dcd89506962933719 ("ARM: dma-mapping: add support for IOMMU mapper"). In meantime ARM64 got a new, slightly improved implementation provided by Robin Murphy in commit 13b8629f651164d71f4d38b821925f93ba4236c8 ("arm64: Add IOMMU dma_ops").
Both implementations are very similar thus their unification is desired to avoid duplicating future works and simplify code, which uses this layer on both architectures. In this patchset I've selected the new implementation (from ARM64 architecture) as a base. This means that ARM-specific, old interface (arm_iommu_* functions) for configuring IOMMU domains will be no longer available and its users have to be converted to new API.
Besides lack of old interface, the second difference is additional requirements for IOMMU drivers. New code relies on the support for IOMMU_DOMAIN_DMA and default IOMMU domain, which is automatically attached by the IOMMU core.
The new code also assumes that the IOMMU-based DMA-mapping ops are mainly configured from arch_setup_dma_ops() function, which means that the IOMMU driver should provide needed of_xlate callbacks and initialize IOMMU ops for device nodes. However it should be also possible to initialize IOMMU-based DMA-mapping ops for client devices directly from IOMMU drivers by calling common_iommu_setup_dma_ops() (some drivers used such approach).
IOMMU drivers should be also aware of the fact that the default domain is attached via device_attach and then device_attach callback can be called once again with different domain without previous detach from default domain. For more information on this issue, see the following thread: https://lists.linaro.org/pipermail/linaro-mm-sig/2016-February/004625.html
Currently there are 4 users of the old arm_iommu_* interface: 1. Exynos DRM driver 2. Rockchip DRM driver 3. OMAP3 ISP camera driver 4. Renesas VMSA-compatible IPMMU driver
In this patchset I've converted Exynos DRM driver for the new API (patch 1). This required some changes in the memory management model inside the driver and removal of some hacks, which were used to setup IOMMU-based DMA-mapping ops on the 'exynos-drm' virtual device and common IOMMU domain for all Exynos DRM sub-devices, those changes have been posted separately here: http://www.spinics.net/lists/dri-devel/msg100861.html Rockchip DRM driver requires similar conversion.
Converting OMAP3 ISP camera driver to new API requires adding support for IOMMU groups to OMAP IOMMU driver, because the new DMA/IOMMU code used IOMMU_DOMAIN_DMA type domains and default groups.
Renesas IPMMU driver needs also to be extended with IOMMU_DOMAIN_DMA domain type support. It can also be prepared for IOMMU_OF_DECLARE and of_xlate callback-based initialization to let core to automatically setup of IOMMU-based DMA mapping implementation.
Patch 2 moves existing code from arch/arm64 to drivers/iommu and introduces some minor changes in function names - mainly adding arch_ prefix to some dma-mapping internal functions, which stay in arch/arm64/ (functions of similar names are present in arch/arm). Patch 3 adapts ARM architecture for the common code.
I would like to get your comments on the proposed approach. There is still some work that need to be done to convert remaining users of the old API and updating IOMMU drivers to the new API requirements. This change need to be tested on the all affected ARM sub-architectures.
Right now patches were tested on only Exynos based boards: ARM 32bit: Exynos4412 and Exynos5422 boards and ARM 64 bit Exnyos 5433 (with some out-of-tree DTS).
To ease testing I've prepared a branch with all the patches needed (there are all needed patches for Exynos subarch, which have been posted as separate patchsets): https://git.linaro.org/people/marek.szyprowski/linux-srpol.git v4.5-dma-iommu-unification
Patches are based on Linux v4.5-rc4 vanilla tree.
Best regards Marek Szyprowski Samsung R&D Institute Poland
Patch summary:
Marek Szyprowski (3): drm/exynos: rewrite IOMMU support code iommu: dma-iommu: move IOMMU/DMA-mapping code from ARM64 arch to drivers iommu: dma-iommu: use common implementation also on ARM architecture
arch/arm/Kconfig | 22 +- arch/arm/include/asm/device.h | 9 - arch/arm/include/asm/dma-iommu.h | 37 - arch/arm/include/asm/dma-mapping.h | 59 +- arch/arm/mm/dma-mapping.c | 1158 +---------------------------- arch/arm64/include/asm/dma-mapping.h | 39 +- arch/arm64/mm/dma-mapping.c | 491 +----------- drivers/gpu/drm/exynos/Kconfig | 2 +- drivers/gpu/drm/exynos/exynos_drm_drv.c | 7 +- drivers/gpu/drm/exynos/exynos_drm_drv.h | 2 +- drivers/gpu/drm/exynos/exynos_drm_iommu.c | 91 ++- drivers/gpu/drm/exynos/exynos_drm_iommu.h | 2 +- drivers/gpu/drm/rockchip/Kconfig | 1 + drivers/iommu/Kconfig | 1 + drivers/iommu/Makefile | 2 +- drivers/iommu/dma-iommu-ops.c | 471 ++++++++++++ drivers/media/platform/Kconfig | 1 + include/linux/dma-iommu.h | 14 + 18 files changed, 679 insertions(+), 1730 deletions(-) delete mode 100644 arch/arm/include/asm/dma-iommu.h create mode 100644 drivers/iommu/dma-iommu-ops.c