Quoting Bill Huang (2013-03-19 21:39:44) > On Wed, 2013-03-20 at 11:31 +0800, Mike Turquette wrote: > > Quoting Bill Huang (2013-03-19 19:55:49) > > > On Wed, 2013-03-20 at 01:01 +0800, Mike Turquette wrote: > > > > Quoting Bill Huang (2013-03-19 06:28:32) > > > > > Add notifier calls in clk_prepare and clk_unprepare so drivers which > > > > > are > > > > > interested in knowing that clk_prepare/unprepare call can act > > > > > accordingly. > > > > > > > > > > The existing "clk_set_rate" notifier is not enough for normal DVFS > > > > > inplementation since clock might be enabled/disabled at runtime. > > > > > Adding > > > > > these notifiers is useful on DVFS core which take clk_prepare as a > > > > > hint > > > > > on that the notified clock might be enabled later so it can raise > > > > > voltage > > > > > to a safe level before enabling the clock, and take clk_unprepare as a > > > > > hint that the clock has been disabled and is safe to lower the > > > > > voltage. > > > > > > > > > > The added notifier events are: > > > > > > > > > > PRE_CLK_PREPARE > > > > > POST_CLK_PREPARE > > > > > ABORT_CLK_PREPARE > > > > > PRE_CLK_UNPREPARE > > > > > POST_CLK_UNPREPARE > > > > > > > > > > Signed-off-by: Bill Huang <bilhu...@nvidia.com> > > > > > > > > I'm still not sure about this approach. Based on feedback I got from > > > > Linaro Connect I am not convinced that scaling voltage through clk > > > > rate-change notifiers is the right way to go. As I understand it this > > > > patch only exists for that single purpose, so if the voltage-notifier > > > > idea gets dropped then I will not take this patch in. > > > > > > > Thanks Mike, actually we won't use your "clk: notifier handler for > > > dynamic voltage scaling" patch instead we are trying to port our DVFS > > > into Non-CPU DVFS framework "devfreq" which will need to hook those > > > notifiers, without the clock notifiers been extended the framework is > > > useless for us since we cannot do polling due to the fact that polling > > > is not in real time. If it ended up extending the notifiers cannot > > > happen then the only choice for us I think would be giving up "devfreq" > > > and implement them in Tegra's "clk_hw". > > > > I'm familiar with the devfreq framework. Can you explain further how > > you plan to use devfreq with the clock notifiers? What does the call > > graph look like? > > > The call graph will look like this, when any DVFS interested clock rate > changes (including enable and disable) happen -> Tegra devfreq clock > notifier is called -> call into update_devfreq if needed -> in > update_devfreq it will call into .get_target_freq in Tegra > "devfreq_governor" -> and then call into .target of tegra > devfreq_dev_profile to set voltage and done. More details are as below. > > We'll create devfreq driver for Tegra VDD_CORE rail, and the safe > voltage level of the rail is determined by tens of clocks (2d, 3d, > mpe,...), all the frequency ladders of those clocks are defined in DT > also the operating points for VDD_CORE is declared in DT where its > frequency will be more of a virtual clock or index. > > operating-points = < > /* virtual-kHz uV */ > 0 950000 > 1 1000000 > 2 1050000 > 3 1100000 > 4 1150000 > 5 1200000 > 6 1250000 > 7 1300000 > 8 1350000 > > Register a Tegra governor where the callback .get_target_freq is the > function to determine the overall frequency it can go to, and > the .target callback in "devfreq_dev_profile" will be the function > really do the voltage scaling. > > Tegra devfreq driver will register clock notifiers on all its interested > clock and hence when any of those clock rate changes, disabled, enabled, > we'll specifically call update_devfreq in the notifier.
Thank you for the explanation. Do you plan to use actual devfreq governors (like simple-ondemand, or something custom) for changing OPPs, or do you just plan to use the clock framework as a trigger for DVFS? Regards, Mike _______________________________________________ linaro-dev mailing list linaro-dev@lists.linaro.org http://lists.linaro.org/mailman/listinfo/linaro-dev
