Messages in this thread | | | Date | Wed, 6 Nov 2013 16:21:48 -0800 | Subject | Re: Async runtime put in __device_release_driver() | From | Kevin Hilman <> |
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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.
Kevin
> --- > 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); >
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