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    Subject[PATCH V2] ARM: OMAP2+: omap_device: maintain sane runtime pm status around suspend/resume
    Date
    OMAP device hooks around suspend|resume_noirq ensures that hwmod
    devices are forced to idle using omap_device_idle/enable as part of
    the last stage of suspend activity.

    For a device such as i2c who uses autosuspend, it is possible to enter
    the suspend path with dev->power.runtime_status = RPM_ACTIVE.

    As part of the suspend flow, the generic runtime logic would increment
    it's dev->power.disable_depth to 1. This should prevent further
    pm_runtime_get_sync from succeeding once the runtime_status has been
    set to RPM_SUSPENDED.

    Now, as part of the suspend_noirq handler in omap_device, we force the
    following: if the device status is !suspended, we force the device
    to idle using omap_device_idle (clocks are cut etc..). This ensures
    that from a hardware perspective, the device is "suspended". However,
    runtime_status is left to be active.

    *if* an operation is attempted after this point to
    pm_runtime_get_sync, runtime framework depends on runtime_status to
    indicate accurately the device status, and since it sees it to be
    ACTIVE, it assumes the module is functional and returns a non-error
    value. As a result the user will see pm_runtime_get succeed, however a
    register access will crash due to the lack of clocks.

    To prevent this from happening, we should ensure that runtime_status
    exactly indicates the device status. As a result of this change
    any further calls to pm_runtime_get* would return -EACCES (since
    disable_depth is 1). On resume, we restore the clocks and runtime
    status exactly as we suspended with.

    Reported-by: J Keerthy <j-keerthy@ti.com>
    Signed-off-by: Nishanth Menon <nm@ti.com>
    Acked-by: Rajendra Nayak <rnayak@ti.com>
    Acked-by: Kevin Hilman <khilman@linaro.org>
    ---
    Changes in V2 (resend):
    - dropped the unnecessary flag for runtime status restore
    - picked up kevin's ack from https://patchwork.kernel.org/patch/3168371/

    v1: https://patchwork.kernel.org/patch/3154501/

    patch baseline: V3.12 tag (also applies on linux-next next-20131107 tag)

    Logs from 3.12 based vendor kernel:
    Before: http://pastebin.com/m5KxnB7a
    After: http://pastebin.com/8AfX4e7r
    The discussion on cpufreq side of the story which triggered this scenario:
    http://marc.info/?l=linux-pm&m=138263811321921&w=2

    Tested on TI vendor kernel (with dt boot):
    AM335x: evm, BBB, sk, BBW
    OMAP5uEVM, DRA7-evm

    arch/arm/mach-omap2/omap_device.c | 5 +++--
    1 file changed, 3 insertions(+), 2 deletions(-)

    diff --git a/arch/arm/mach-omap2/omap_device.c b/arch/arm/mach-omap2/omap_device.c
    index b69dd9a..f97b34b 100644
    --- a/arch/arm/mach-omap2/omap_device.c
    +++ b/arch/arm/mach-omap2/omap_device.c
    @@ -621,6 +621,7 @@ static int _od_suspend_noirq(struct device *dev)

    if (!ret && !pm_runtime_status_suspended(dev)) {
    if (pm_generic_runtime_suspend(dev) == 0) {
    + pm_runtime_set_suspended(dev);
    omap_device_idle(pdev);
    od->flags |= OMAP_DEVICE_SUSPENDED;
    }
    @@ -634,10 +635,10 @@ static int _od_resume_noirq(struct device *dev)
    struct platform_device *pdev = to_platform_device(dev);
    struct omap_device *od = to_omap_device(pdev);

    - if ((od->flags & OMAP_DEVICE_SUSPENDED) &&
    - !pm_runtime_status_suspended(dev)) {
    + if (od->flags & OMAP_DEVICE_SUSPENDED) {
    od->flags &= ~OMAP_DEVICE_SUSPENDED;
    omap_device_enable(pdev);
    + pm_runtime_set_active(dev);
    pm_generic_runtime_resume(dev);
    }

    --
    1.7.9.5


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