• Ulf Hansson's avatar
    PM / Domains: Fix initial default state of the need_restore flag · 67732cd3
    Ulf Hansson authored
    The initial state of the device's need_restore flag should'nt depend on
    the current state of the PM domain. For example it should be perfectly
    valid to attach an inactive device to a powered PM domain.
    
    The pm_genpd_dev_need_restore() API allow us to update the need_restore
    flag to somewhat cope with such scenarios. Typically that should have
    been done from drivers/buses ->probe() since it's those that put the
    requirements on the value of the need_restore flag.
    
    Until recently, the Exynos SOCs were the only user of the
    pm_genpd_dev_need_restore() API, though invoking it from a centralized
    location while adding devices to their PM domains.
    
    Due to that Exynos now have swithed to the generic OF-based PM domain
    look-up, it's no longer possible to invoke the API from a centralized
    location. The reason is because devices are now added to their PM
    domains during the probe sequence.
    
    Commit "ARM: exynos: Move to generic PM domain DT bindings"
    did the switch for Exynos to the generic OF-based PM domain look-up,
    but it also removed the call to pm_genpd_dev_need_restore(). This
    caused a regression for some of the Exynos drivers.
    
    To handle things more properly in the generic PM domain, let's change
    the default initial value of the need_restore flag to reflect that the
    state is unknown. As soon as some of the runtime PM callbacks gets
    invoked, update the initial value accordingly.
    
    Moreover, since the generic PM domain is verifying that all devices
    are both runtime PM enabled and suspended, using pm_runtime_suspended()
    while pm_genpd_poweroff() is invoked from the scheduled work, we can be
    sure of that the PM domain won't be powering off while having active
    devices.
    
    Do note that, the generic PM domain can still only know about active
    devices which has been activated through invoking its runtime PM resume
    callback. In other words, buses/drivers using pm_runtime_set_active()
    during ->probe() will still suffer from a race condition, potentially
    probing a device without having its PM domain being powered. That issue
    will have to be solved using a different approach.
    
    This a log from the boot regression for Exynos5, which is being fixed in
    this patch.
    
    ------------[ cut here ]------------
    WARNING: CPU: 0 PID: 308 at ../drivers/clk/clk.c:851 clk_disable+0x24/0x30()
    Modules linked in:
    CPU: 0 PID: 308 Comm: kworker/0:1 Not tainted 3.18.0-rc3-00569-gbd9449f-dirty #10
    Workqueue: pm pm_runtime_work
    [<c0013c64>] (unwind_backtrace) from [<c0010dec>] (show_stack+0x10/0x14)
    [<c0010dec>] (show_stack) from [<c03ee4cc>] (dump_stack+0x70/0xbc)
    [<c03ee4cc>] (dump_stack) from [<c0020d34>] (warn_slowpath_common+0x64/0x88)
    [<c0020d34>] (warn_slowpath_common) from [<c0020d74>] (warn_slowpath_null+0x1c/0x24)
    [<c0020d74>] (warn_slowpath_null) from [<c03107b0>] (clk_disable+0x24/0x30)
    [<c03107b0>] (clk_disable) from [<c02cc834>] (gsc_runtime_suspend+0x128/0x160)
    [<c02cc834>] (gsc_runtime_suspend) from [<c0249024>] (pm_generic_runtime_suspend+0x2c/0x38)
    [<c0249024>] (pm_generic_runtime_suspend) from [<c024f44c>] (pm_genpd_default_save_state+0x2c/0x8c)
    [<c024f44c>] (pm_genpd_default_save_state) from [<c024ff2c>] (pm_genpd_poweroff+0x224/0x3ec)
    [<c024ff2c>] (pm_genpd_poweroff) from [<c02501b4>] (pm_genpd_runtime_suspend+0x9c/0xcc)
    [<c02501b4>] (pm_genpd_runtime_suspend) from [<c024a4f8>] (__rpm_callback+0x2c/0x60)
    [<c024a4f8>] (__rpm_callback) from [<c024a54c>] (rpm_callback+0x20/0x74)
    [<c024a54c>] (rpm_callback) from [<c024a930>] (rpm_suspend+0xd4/0x43c)
    [<c024a930>] (rpm_suspend) from [<c024bbcc>] (pm_runtime_work+0x80/0x90)
    [<c024bbcc>] (pm_runtime_work) from [<c0032a9c>] (process_one_work+0x12c/0x314)
    [<c0032a9c>] (process_one_work) from [<c0032cf4>] (worker_thread+0x3c/0x4b0)
    [<c0032cf4>] (worker_thread) from [<c003747c>] (kthread+0xcc/0xe8)
    [<c003747c>] (kthread) from [<c000e738>] (ret_from_fork+0x14/0x3c)
    ---[ end trace 40cd58bcd6988f12 ]---
    
    Fixes: a4a8c2c4 (ARM: exynos: Move to generic PM domain DT bindings)
    Reported-and-tested0by: Sylwester Nawrocki <s.nawrocki@samsung.com>
    Reviewed-by: default avatarSylwester Nawrocki <s.nawrocki@samsung.com>
    Reviewed-by: default avatarKevin Hilman <khilman@linaro.org>
    Signed-off-by: default avatarUlf Hansson <ulf.hansson@linaro.org>
    Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    67732cd3
pm_domain.h 9.53 KB