Hi, On Tue, Sep 16, 2014 at 8:20 AM, Javier Martinez Canillas <javier@xxxxxxxxxxxx> wrote: > Hello Daniel, > > On Tue, Sep 16, 2014 at 5:03 PM, Daniel Drake <drake@xxxxxxxxxxxx> wrote: >> On Tue, Sep 16, 2014 at 7:48 AM, Javier Martinez Canillas >> <javier@xxxxxxxxxxxx> wrote: >>>> Clock list for s3c-rtc device: >>>> - rtc : CLK_RTC of CLK_GATE_IP_PERIR is gate clock for RTC. >>>> - rtc_src : XrtcXTI is 32.768.kHz source clock for RTC. >>> >>> Is this RTC source clock needed for all Exynos SoCs? >> >> It is at least needed on Exynos4412, which has the XrtcXTI thing >> exactly as you describe. However the very standard setup there is to >> hook it up to the CP clock output of the MAX76686 PMIC. This CP clock >> is on by default, so you can potentially live without that detail >> being present in the DT. >> > > Thanks for confirming for Exynos4412, I just answered my own email > saying that I found to be needed on Exynos5420 as well and as you > said, it was just working because the Maxim clocks were left on by > default. > >> However... one small issue with this setup is that when you enable >> CONFIG_COMMON_CLK_MAX77686, the CP clock gets exposed in Linux's >> common clock framework, and Linux then turns it off because it >> believes it is unused. Then the RTC stops ticking. >> > > Indeed, this is an issue about relying on default state. We had a > quite long discussion a couple of weeks ago about simplefb relying on > clocks and regulators left enabled by the bootloader but once these > were know to the kernel, the frameworks disable them because were > unused making simplefb to fail. > >> So the rtc_src idea would also be good for Exynos4412. Maybe it would >> make sense to drop the needs_src_clk flag, and simply require/enable >> the src clock whenever it is present in the DT. >> > > That sounds more sensible to me as well. I wonder what should happen > in this case with DT backward compatibility though. But as you said, > the external clock is required and the kernel will disable this clock > once is know to the CCF since is not used so maybe will be hard to > maintain DT backward compatibility in this case. I think you can turn off CONFIG_COMMON_CLK_MAX77686 and then this clock will be left at whatever the bootloader set it to, right? Then there will be no auto-disabling by the CCF and the RTC will work. That's one argument for making the clock "optional". NOTE: I don't think that the builtin RTC is terribly important for any exynos-based Chromebooks that I'm aware of. We rely on the RTC that's part of the Maxim PMIC itself and pretty much ignore the one built-in to the exynos. I think there are some cases it was used (as a fallback wakeup source in certain test scripts), but nothing very important. -Doug -- To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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