On Wed, Mar 21, 2012 at 7:29 PM, Hiremath, Vaibhav <hvaibhav@xxxxxx> wrote: > On Mon, Mar 19, 2012 at 17:14:30, 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. >> > >> > >> > 2) Let the current code be as is, means, the clocksource registration will >> > Happened based on "#ifdef CONFIG_OMAP_32K_TIMER" and this option >> > selection will be Controlled by Kconfig rules. >> >> How about the 3rd option? >> >> 3), take the way in your patch 1) at default, but will switch to >> register dmtimer >> directly and bypass 32k-counter if user need it via kernel parameter. >> >> As far as I can think of, the situations required for dmtimer are high-frequency >> perf sample and high precision trace points, so looks it is OK to take >> 32k-counter >> at default. >> > But if you register both the timers (dmtimer & 32ksync), then initially kernel will only pick up dmtimer, as this has better rating. And late in Looks not so, I found that 32ksync is always selected as the default clocksource if both are registered. > the boot sequence clocksource switch will happen, base on > kernel parameter (clocksource=). > > So logically dmtimer will be always used as a default here. Not so at least on my Pandaboard. Thanks, -- Ming Lei -- 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
