On 2 May 2014 16:58, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: > Hi Ulf, Tomasz, > > On Fri, May 2, 2014 at 10:13 AM, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote: >>>>> +static int of_clk_register(struct device *dev, struct clk *clk) >>>>> +{ >>>>> + int error; >>>>> + >>>>> + if (!dev->pm_domain) { >>>>> + error = pm_clk_create(dev); >>>>> + if (error) >>>>> + return error; >>>>> + >>>>> + dev->pm_domain = &of_clk_pm_domain; >>>> >>>> >>>> I am concerned about how this will work in conjunction with the >>>> generic power domain. >>>> >>>> A device can't reside in more than one pm_domain; thus I think it >>>> would be better to always use the generic power domain and not have a >>>> specific one for clocks. Typically the genpd should invoke >>>> pm_clk_resume|suspend from it's runtime PM callbacks. >>> >>> I'm not sure about this. A typical use case would be to gate clocks ASAP and >>> then wait until device is idle long enough to consider turning off the power >>> domain worthwhile. Also sometimes we may want to gate the clocks, but >>> prevent power domain from being powered off to retain hardware state (e.g. >>> because there is no way to read it and restore later). >> >> So, in principle you prefer to have driver's handle clock gating to >> save power from their runtime PM callbacks, instead of from the power >> domain, right? Just to clarify, that's my view as well. > > If there's both a gate clock and a power domain, and the driver's Runtime PM > callbacks handle clock gating, who's handling the power domain? This is my view, not sure everybody agrees :-) 1. If you have a hardware power domain you need to implement a pm_domain (preferably use the generic power domain). 2. If you don't have a hardware power domain, but still cares about having a centralized solution for dev_pm_qos - you may use the generic power domain, since it supports this. 3. If none of the above, you don't need a pm_domain at all. Kind regards Ulf Hansson > > Gr{oetje,eeting}s, > > Geert (still trying to fit all pieces of the > puzzle together) > > -- > Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx > > In personal conversations with technical people, I call myself a hacker. But > when I'm talking to journalists I just say "programmer" or something like that. > -- Linus Torvalds -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html