"Sripathy, Vishwanath" <vishwanath.bs@xxxxxx> writes: > Kevin, > >> -----Original Message----- >> From: linux-omap-owner@xxxxxxxxxxxxxxx [mailto:linux-omap- >> owner@xxxxxxxxxxxxxxx] On Behalf Of Kevin Hilman >> Sent: Tuesday, December 22, 2009 9:26 PM >> To: Reddy, Teerth >> Cc: Dasgupta, Romit; linux-omap@xxxxxxxxxxxxxxx >> Subject: Re: [PATCH] OMAP3: PM: Dynamic calculation of SDRC clock stabilization >> delay >> >> "Reddy, Teerth" <teerth@xxxxxx> writes: >> >> > Kevin, >> > >> >> >> >> Here's an uncompiled, untested version of 'measure_sram_delay' using >> >> the DM Timer API: >> >> >> >> unsigned int measure_sram_delay(unsigned int loop) >> >> { >> >> unsigned long start, end, flags; >> >> void (*_omap3_sram_delay)(unsigned long); >> >> _omap3_sram_delay = omap_sram_push(__sram_wait_delay, >> >> __sram_wait_delay_sz); >> >> >> >> gpt = omap_dm_timer_request(); >> >> if (!gpt) >> >> pr_err("foo"); >> >> omap_dm_timer_set_source(gpt, OMAP_TIMER_SRC_SYS_CLK); >> >> omap_dm_timer_set_load_start(gptimer, 0, 0); >> >> >> >> local_irq_save(flags); >> >> start = omap_dm_timer_read_counter(gpt); >> >> _omap3_sram_delay(loop); >> >> end = omap_dm_timer_read_counter(gpt); >> >> local_irq_restore(flags); >> >> >> >> omap_dm_timer_stop(gpt); >> >> omap_dm_timer_free(gpt); >> >> >> >> return end - start; >> >> } >> >> >> > >> > I see one shortcoming with this approach. The DVFS happens even >> > before the gp timers are initialized, while the kernel boots. >> >> This is a bug. DVFS should be prevented until system is initialized. >> > > > I think DVFS is triggered when CPU Freq driver gets > initialized. Depending on the default governor cpufreq tries to > scale the frequency which triggers DVFS. Correct. > So do you mean to say that cpufreq initialization should be > prevented till GPTimer is initialized? Basically, yes. You need to calibrate the delay before you can do DVFS, so what I mean is that you need to request your GPtimer, and do your delay measurements using the GPtimer before you enable DVFS (register CPUfreq.) Also, please be sure to stop/free the GPtimer when done, otherwise it will prevent idle. Kevin -- 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
