On Wednesday, October 08, 2014 02:00:50 PM Ulf Hansson wrote: > On 7 October 2014 21:09, Geert Uytterhoeven <ge...@linux-m68k.org> wrote: > > Hi Ulf, > > > > On Tue, Sep 30, 2014 at 2:43 PM, Ulf Hansson <ulf.hans...@linaro.org> wrote: > >> Instead, let's improve the situation, by preventing genpd from powering > >> off any of the PM domains until late_init. At that point genpd already > >> tries to power off unused PM domains, so it seems like a decent match. > > > > Note that powering off unused PM domains is currently limited to > > CONFIG_PM_RUNTIME=y. > > If CONFIG_PM_RUNTIME is disabled, unused PM domains are not powered down, > > and may even stay powered-up during system suspend. > > Right. That's obviously not an acceptable behaviour, we can do better. > > > > > With CONFIG_PM_RUNTIME=y, we have: > > A1. All PM domains are powered up during initialization. > > A2. After initialization, all unused PM domains are powered down by the > > genpd_poweroff_unused() late_initcall. > > "unused" means PM domains containing no active devices and no active > > subdomains. I.e. PM domains containing (a) only suspended devices, or > > (b) no[*] devices at all will be powered down. > > A3. PM domains will be powered up or down, depending on devices moving > > from > > inactive to active state, or vice versa. This includes system suspend, > > which can be considered some form of devices moving to an inactive > > state. > > > > In contrast, with CONFIG_PM_RUNTIME=n, we have: > > B1. All PM domains are powered up during initialization, > > B2. After initialization, PM domains just stay powered up, > > B3. PM domains will be powered down on system suspend, and powered up on > > system resume, based on the dev_pm_ops of the PM domain each device > > belongs to. > > > > While operation A2 is PM domain-centric (it walks the list of genpd > > domains), > > A3 and B3 are device-centric (A3 operates on one specific device, B3 walks > > the > > list of devices). > > Hence B3 never touches PM domains that don't contain any devices[*]. > > So these PM domains are kept powered-up if CONFIG_PM_RUNTIME=n, even on > > system suspend. > > > > Shouldn't PM domains without devices be powered down at some point? > > When? In B2, or in B3? > > I agree with Rafael and Sylwester, that it would be an advantage if PM > domains can be initialized in powered off state. Simply because, those > may then be left in powered off state all the time, if they are > unused. > > That's been my long term approach, but let's see if we can get there > without the intermediate step proposed in this patchset... > > Now, to support the above and to solve the race conditions, we need to > be able to power up the PM domain, prior probing of a device. I am > thinking of a solution aimed to affect subsystem level code (buses) > and not drivers, since we need keep the impact on a reasonable level.
That sounds like a good approach to me. Also that should work regardless of whether or not the drivers in question implement runtime PM callbacks. -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
