On Rockchip SoCs, the IOMMUs are located inside the same power domains as IP blocks using them. This means that as soon as we runtime suspend such IP block, causing the power domain to be powered off, the IOMMU would also be powered off, losing all its state. This means that whenever the power domain is being powered off, the IOMMU driver needs to be able to deinitialize the hardware and whenever the domain is being powered on, it needs to restore all the state, so the consumer device is able to perform memory transactions. The solution proposed here revives the idea of PM domain notifiers submitted originally by Samsung's Sylwester Nawrocki and Marek Szyprowski in [1]. The main benefit of this idea that it is very simple, adding just 84 lines of code, but effective and also useful for other purposes, what can be seen in thread [2] and [3]. Moreover, it lets us avoid adding device specific code (in this case specific to single IOMMU type) to power domain drivers, which can be used for more devices than just IOMMU and which may vary between platforms using the same IOMMU driver. The IOMMU-specific part of the solution simply uses the pre-power-off and post-power-on notifications to do the necessary setup without the need of any action from inside drivers of devices behind the IOMMU, so all the code specific to this particular IOMMU type stays outside other drivers that should not rely on being run with a particular type of IOMMU (and often even SoC). Tested with a custom board based on RK3288 SoC. [1] http://thread.gmane.org/gmane.linux.kernel.samsung-soc/36079/focus=346956 [2] http://thread.gmane.org/gmane.linux.power-management.general/51993/focus=39158 [3] http://marc.info/?l=linux-pm&m=136448756308203&w=2 Sylwester Nawrocki (1): pm: Add PM domain notifications Tomasz Figa (1): iommu: rockchip: Handle system-wide and runtime PM Documentation/power/notifiers.txt | 14 +++ drivers/base/power/domain.c | 50 +++++++++ drivers/iommu/rockchip-iommu.c | 208 +++++++++++++++++++++++++++++++------- include/linux/pm_domain.h | 20 ++++ 4 files changed, 256 insertions(+), 36 deletions(-) -- 2.2.0.rc0.207.ga3a616c
