On Fri, 2013-03-15 at 13:22 +0800, Stephen Warren wrote: > On 03/14/2013 07:20 PM, Bill Huang wrote: > > On Fri, 2013-03-15 at 01:54 +0800, Stephen Warren wrote: > >> On 03/14/2013 03:28 AM, Bill Huang wrote: > >>> On Thu, 2013-03-14 at 17:21 +0800, Peter De Schrijver wrote: > >>>> On Thu, Mar 14, 2013 at 03:15:11AM +0100, Bill Huang wrote: > >>>> > >>>>> I don't think deferring will work either, considering the usage of DVFS, > >>>>> device voltage is tightly coupled with frequency, when clock rate is > >>>>> about to increase, we have to boost voltage first and we can lower the > >>>>> voltage after the clock rate has decreased. All the above sequence have > >>>>> to be guaranteed or you might crash, so deferring not only make thing > >>>>> complicated in controlling the order but also hurt performance. > >>>> > >>>> But we could use notifiers in clk_prepare/clk_unprepare to set the > >>>> voltage no? > >>>> As clk_prepare/clk_unprepare have to be called before clk_enable or after > >>>> clk_disable, the voltage can be raised to a safe level, before the clock > >>>> becomes active. > >>> > >>> Thanks Peter, actually I'm just about to propose my v2 RFC which add > >>> notifier in clk_prepare/clk_unprepare. > >> > >> Can't clk_set_rate() be called while the clock is prepared, or even > >> enabled? I don't see how your proposal would work. > > > > I think it works with just a little sacrifice on saving more power but > > that's related minor. Taking clk_prepare as an indicator on that clock > > will be enabled later, so we can raise the voltage to a safe level > > (according to the current rate or maybe default rate when clk_prepare is > > called, some time late when clk_set_rate() is called we can adjust again > > according to the requested rate change) > > Is clk_set_rate() only legal to call in non-atomic contexts then? The > header file doesn't say, although I guess since many other functions > explicitly say they can't, then by omission it can...
I think clk_set_rate can only be called in non-atomic contexts since there are existing non-atomic clock notifier hooked in it. _______________________________________________ linaro-dev mailing list linaro-dev@lists.linaro.org http://lists.linaro.org/mailman/listinfo/linaro-dev
