On Tue, 26 Jun 2012, Tomi Valkeinen wrote:
> > Failure to suspend a device should not be regarded as particularly bad,
> > because it doesn't affect the device's functionality. That's true even
> > when CONFIG_RUNTIME_PM is enabled.
>
> This makes sense. So if CONFIG_RUNTIME_PM=n, using pm_runtime_get_sync()
> will return 1, meaning the HW is already enabled, and using
> pm_runtime_put_sync() will return -ENOSYS, meaning the hardware cannot
> be suspended.
>
> With CONFIG_RUNTIME_PM=y, it's a bit more complex. If I read the code
> correctly, when I call pm_runtime_get_sync(), the usage counter is
> always increased, even if the pm_runtime_resume() fails. So a get()
> needs to be always matched with a put(), even if get() has returned an
> error.
Right. Of course, it doesn't hurt to match a get() with a put() even
when CONFIG_RUNTIME_PM=n.
> But if pm_runtime_get_sync() returns an error, it means the HW has not
> been resumed successfully, and is not operational, so the code should
> bail out somehow. So basically I'd use this kind of pattern everywhere I
> use pm_runtime_get_sync():
>
> ---
>
> r = pm_runtime_get_sync(dev);
> if (r < 0) {
> pm_runtime_put_sync(dev);
Here you could just as well call pm_runtime_put_noidle(). Since the
device wasn't resumed, the put operation doesn't need to try to suspend
it.
> /* handle error */
> return -ESOMETHING;
> }
>
> /* do the work */
>
> pm_runtime_put_sync(dev);
>
> ---
>
> Is this correct?
Yep, you've got it.
Alan Stern
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