On Wed, Mar 21, 2012 at 5:12 PM, Hiremath, Vaibhav <hvaibhav@xxxxxx> wrote: > On Mon, Mar 19, 2012 at 17:45:32, Shilimkar, Santosh wrote: >> On Monday 19 March 2012 05:14 PM, Ming Lei wrote: >> > On Mon, Mar 19, 2012 at 7:11 PM, Hiremath, Vaibhav <hvaibhav@xxxxxx> wrote: >> >> >> >> I think you made very good point here. With the above patch, we are almost missing the capability of registering dmtimer as a clocksource for OMAP. >> >> It will always use 32k-counter, and never fall back to dmtimer. >> >> >> >> Then the only options we have here is, >> >> >> >> 1) Register both the timers, 32k-counter and dmtimer for clocksource; let >> >> Kernel pick up best rating clocksource out of these two. >> >> >> >> In case of OMAP1/2/3/4, kernel will use dmtimer, since it has better >> >> Rating. User can choose the 32k-counter clocksource via bootargs. >> >> >> >> Impact: without bootargs for clocksource selection, kernel will choose >> >> dmtimer, impacting loss of time during suspend/resume. >> >> >> This is the right option. The problem is gptimer clocksource >> doesn't work across power transitions and hence it is broken. >> >> Even for the perf, with PM enabled, dmtimer can't be used or it needs >> to be used with 32KHz clock which makes it no better than sync timer. >> >> So here keeping 32K sync timer is default clocksource makes sense since >> it is the only working and viable option. >> >> So what can be done is register both 32K and gptimer together but make >> gptimer clocksource registration depends on PM enabled. >> >> This should solve all the needs I guess. >> > > I am not sure this will work on all platforms, for example, AM33XX, where > We do not have 32ksync timer available, but we need PM support. Also, I > personally think, we should not again use compile time option here. > Why not ? If 32ksync timer is not available, don't register it. Then in AM case you just have one clock-source. I am against the idea of making gptimer as the default and asking user to choose sync32k from command-line. Btw, if you need PM, how are you going to use GPTIMER as a clocksource. Note sys-clock is generally stopped in low power states. So that leaves you option with using gptimer with 32K clock and in that case, GPTIMER is not a better clock-source compare to 32K sync timer and so shouldn't be the rating. Regards Santosh -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
