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    SubjectRe: [PATCH v8 3/5] amba: Don't unprepare the clocks if device driver wants IRQ safe runtime PM
    On Sat, Nov 01, 2014 at 12:55:14AM +0000, Russell King - ARM Linux wrote:
    > On Sat, Nov 01, 2014 at 01:45:47AM +0100, Rafael J. Wysocki wrote:
    > > On Monday, October 20, 2014 11:04:46 AM Krzysztof Kozlowski wrote:
    > > > @@ -198,8 +217,10 @@ static int amba_probe(struct device *dev)
    > > > pm_runtime_enable(dev);
    > > >
    > > > ret = pcdrv->probe(pcdev, id);
    > > > - if (ret == 0)
    > > > + if (ret == 0) {
    > > > + pcdev->irq_safe = pm_runtime_is_irq_safe(dev);
    > >
    > > This looks racy.
    > >
    > > Is it guaranteed that runtime PM callbacks won't be run for the device
    > > after pcdrv->probe() has returned and before setting pcdev->irq_safe?
    > > If not, inconsistent behavior may ensue.
    >
    > You are absolutely correct. So that knocks that idea on its head.

    Actually, I think we shouldn't give up hope here. Currently, we do this:

    pm_runtime_get_noresume(dev);
    pm_runtime_set_active(dev);
    pm_runtime_enable(dev);

    ret = pcdrv->probe(pcdev, id);

    What we could do is:
    pm_runtime_get_noresume(dev);
    pm_runtime_get_noresume(dev);
    pm_runtime_set_active(dev);
    pm_runtime_enable(dev);

    ret = pcdrv->probe(pcdev, id);
    if (ret == 0) {
    pcdev->irq_safe = pm_runtime_is_irq_safe(dev);
    pm_runtime_put(dev);
    break;
    }
    pm_runtime_disable(dev);
    pm_runtime_set_suspended(dev);
    pm_runtime_put_noidle(dev);
    pm_runtime_put_noidle(dev);

    which would ensure that we hold a usecount until after the probe function
    has returned. Would that work?

    I'll give you that it's pretty horrid.

    Would another possible solution be to remember the irq-safeness in the
    suspend handler, and use that in the resume handler? Resume should
    /always/ undo what the suspend handler previously did wrt clk API stuff.

    --
    FTTC broadband for 0.8mile line: currently at 9.5Mbps down 400kbps up
    according to speedtest.net.


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