On Wed, Aug 09, 2017 at 03:28:22PM +0200, Ulf Hansson wrote:
> The commit 8503ff166504 ("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 commit 8503ff166504
> ("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@xxxxxxxxxxxxxxx> # v4.4+
> Signed-off-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
Applied to for-current, thanks!
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