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The commit8503ff1665("i2c: designware: Avoid unnecessary resuming during system suspend"), may suggest to the PM core to try out the so called direct_complete path for system sleep. In this path, the PM core treats a runtime suspended device as it's already in a proper low power state for system sleep, which makes it skip calling the system sleep callbacks for the device, except for the ->prepare() and the ->complete() callbacks. However, the PM core may unset the direct_complete flag for a parent device, in case its child device are being system suspended before. In this scenario, the PM core invokes the system sleep callbacks, no matter if the device is runtime suspended or not. Particularly in cases of an existing i2c slave device, the above path is triggered, which breaks the assumption that the i2c device is always runtime resumed whenever the dw_i2c_plat_suspend() is being called. More precisely, dw_i2c_plat_suspend() calls clk_core_disable() and clk_core_unprepare(), for an already disabled/unprepared clock, leading to a splat in the log about clocks calls being wrongly balanced and breaking system sleep. To still allow the direct_complete path in cases when it's possible, but also to keep the fix simple, let's runtime resume the i2c device in the ->suspend() callback, before continuing to put the device into low power state. Note, in cases when the i2c device is attached to the ACPI PM domain, this problem doesn't occur, because ACPI's ->suspend() callback, assigned to acpi_subsys_suspend(), already calls pm_runtime_resume() for the device. It should also be noted that this change does not fix commit8503ff1665("i2c: designware: Avoid unnecessary resuming during system suspend"). Because for the non-ACPI case, the system sleep support was already broken prior that point. Cc: <stable@vger.kernel.org> # v4.4+ Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Tested-by: John Stultz <john.stultz@linaro.org> Tested-by: Jarkko Nikula <jarkko.nikula@linux.intel.com> Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com> Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.