Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: Async runtime put in __device_release_driver() | Date | Thu, 07 Nov 2013 02:05:22 +0100 |
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On Wednesday, November 06, 2013 04:21:48 PM Kevin Hilman wrote: > On Wed, Nov 6, 2013 at 4:16 PM, Rafael J. Wysocki <rjw@rjwysocki.net> wrote: > > On Wednesday, November 06, 2013 11:48:24 PM Ulf Hansson wrote: > >> > >> "Rafael J. Wysocki" <rjw@rjwysocki.net> skrev: > >> >On Wednesday, November 06, 2013 05:02:12 PM Alan Stern wrote: > >> >> On Wed, 6 Nov 2013, Rafael J. Wysocki wrote: > >> >> > >> >> > On Wednesday, November 06, 2013 09:51:42 AM Tomi Valkeinen wrote: > >> >> > > On 2013-11-05 23:29, Ulf Hansson wrote: > >> >> > > > On 23 October 2013 12:11, Tomi Valkeinen > >> ><tomi.valkeinen@ti.com> wrote: > >> >> > > >> Hi, > >> >> > > >> > >> >> > > >> I was debugging why clocks were left enabled after removing > >> >omapdss > >> >> > > >> driver, and I found this commit: > >> >> > > >> > >> >> > > >> fa180eb448fa263cf18dd930143b515d27d70d7b (PM / Runtime: Idle > >> >devices > >> >> > > >> asynchronously after probe|release) > >> >> > > >> > >> >> > > >> I don't understand how that is supposed to work. > >> >> > > >> > >> >> > > >> When a driver is removed, instead of using > >> >pm_runtime_put_sync() the > >> >> > > >> commit uses pm_runtime_put(), so the runtime_suspend call is > >> >queued. But > >> >> > > >> who is going to handle the queued suspend call, as the driver > >> >is already > >> >> > > >> removed? At least in my case, obviously nobody, as I only get > >> >> > > >> runtime_resume call in my driver, never the runtime_suspend. > >> >> > > >> > >> >> > > >> Is there something I need to add to my driver to make this > >> >work, or > >> >> > > >> should that part of the patch be reverted? > >> >> > > > > >> >> > > > I believe it is quite common that a device driver calls > >> >> > > > pm_runtime_get_sync as a part of it's remove callback, then it > >> >> > > > explicitly returns it's resources that has been fetched during > >> >probe. > >> >> > > > Like a clk_disable_unprepare for example. > >> >> > > > >> >> > > I guess you mean the driver calls pm_runtime_get_sync _and_ > >> >> > > pm_runtime_put_sync as part of its remove callback? > >> >> > > > >> >> > > Probably bus drivers need to do that, but for memory mapped > >> >devices in a > >> >> > > SoC, I don't think there's normally any need to do > >> >> > > pm_runtime_get/put_sync during the remove callback. > >> >> > > > >> >> > > > The idea behind the change in __device_release_driver, was to > >> >try to > >> >> > > > prevent devices from going active->idle->active and instead > >> >just > >> >> > > > remain active (if possible). > >> >> > > > > >> >> > > > In your case, which seems like a more modern way of > >> >implementing > >> >> > > > "remove", you shall call "pm_runtime_suspend" to make sure the > >> >> > > > runtime_suspend callbacks gets called. > >> >> > > > >> >> > > And as far as I understand, the change creates an explicit > >> >requirement > >> >> > > to do either pm_runtime_get/put_sync or pm_runtime_suspend inside > >> >> > > driver's remove callback. If so, that should be mentioned in big > >> >red > >> >> > > letters in the pm-runtime documentation. > >> >> > > > >> >> > > The runtime_pm.txt doc does mention something related to this > >> >(and btw, > >> >> > > the doc says pm_runtime_put_sync is being called, which is no > >> >longer > >> >> > > true), but nothing clear about how the driver remove callback > >> >must be > >> >> > > implemented. > >> >> > > >> >> > That's correct. > >> >> > > >> >> > > I tried grepping the kernel sources to find out if > >> >pm_runtime_suspend is > >> >> > > widely used to get SoC platform devices to suspend, but it > >> >doesn't seem > >> >> > > like it is. I didn't see pm_runtime_get/put_sync being used in > >> >remove > >> >> > > callbacks widely either, but that was more difficult one to grep. > >> >> > > >> >> > I think your observations are valid, which unfortunately means that > >> >we'll > >> >> > need to revert the commit in question, because it has changed the > >> >behavior > >> >> > that drivers are perfectly fine to expect given the existing > >> >documentation > >> >> > etc. It looks like the change was premature at least. > >> >> > > >> >> > Greg, I wonder if you can queue up a revert of fa180eb448fa for > >> >3.13, or > >> >> > do you want me to do that? > >> >> > >> >> Would it be better to leave the runtime-idle callbacks (invoked > >> >during > >> >> probe) async and revert only the change to __device_release_driver()? > >> >> > >> >> Having an async callback after probe shouldn't cause problems, > >> >because > >> >> the driver will then be bound (assuming the probe succeeded). > >> > > >> >Right. OK, I'll prepare a patch. > >> > >> That seems like a good way forward. > > > > There you go. > > > > --- > > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > > Subject: PM / runtime: Use pm_runtime_put_sync() in __device_release_driver() > > > > Commit fa180eb448fa (PM / Runtime: Idle devices asynchronously after > > probe|release) modified __device_release_driver() to call > > pm_runtime_put(dev) instead of pm_runtime_put_sync(dev) before > > detaching the driver from the device. However, that was a mistake, > > because pm_runtime_put(dev) causes rpm_idle() to be queued up and > > the driver may be gone already when that function is executed. > > That breaks the assumptions the drivers have the right to make > > about the core's behavior on the basis of the existing documentation > > and actually causes problems to happen, so revert that part of > > commit fa180eb448fa and restore the previous behavior of > > __device_release_driver(). > > > > Reported-by: Tomi Valkeinen <tomi.valkeinen@ti.com> > > Fixes: fa180eb448fa (PM / Runtime: Idle devices asynchronously after probe|release) > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > > Cc: 3.10+ <stable@vger.kernel.org> # 3.10+ > > Acked-by: Kevin Hilman <khilman@linaro.org> > > I like this fix since I don't want to add any more requirements to drivers.
OK, I've queued this up for 3.13.
Thanks!
> > --- > > drivers/base/dd.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > Index: linux-pm/drivers/base/dd.c > > =================================================================== > > --- linux-pm.orig/drivers/base/dd.c > > +++ linux-pm/drivers/base/dd.c > > @@ -499,7 +499,7 @@ static void __device_release_driver(stru > > BUS_NOTIFY_UNBIND_DRIVER, > > dev); > > > > - pm_runtime_put(dev); > > + pm_runtime_put_sync(dev); > > > > if (dev->bus && dev->bus->remove) > > dev->bus->remove(dev); > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-pm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center.
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