Hi Tobias, Am 21.11.2016 um 14:33 schrieb Tobias Jakobi: > Hello everyone, > > I was thinking about the following. At the moment we have a suspend OPP > for cpufreq-dt in place for the Exynos4412 SoC (added in > 1605b60ad064c7019db8ade07f0b7bdc8c197b93). The rationale behind is that > the board using the SoC might not have some PMIC reset in place. In case > the board goes into reboot with a low OPP (i.e. low frequency, but also > low core voltage), this results in a hang when the first-stage > bootloaders sets its default core frequency. > > So this is properly handled in the kernel just fine, except for some > corner cases like emergency reboot. > > But some time ago devfreq support for the various busses in the > Exynos4412 was added. On the ODROID boards e.g. this adjust MIF and INT > voltage. > > Let us take the DMC bus. Operating frequency is 100~400MHz and voltage > is 900~1050mV. > > Now let's look at the corresponding board file > (http://git.denx.de/?p=u-boot.git;a=blob;f=board/samsung/odroid/odroid.c#l234) > in upstream u-boot. If I read this correctly DMC is set to 400MHz there. > > Here's the question. Could this, similar to the cpufreq/core frequency > issue, pose a problem when the kernel goes into reboot when DMC is on > the lowest OPP state? > > I'm not saying that it does. This just came to my mind during some > recent discussion. Made a test with # echo performance > /sys/class/devfreq/bus_leftbus/governor # echo performance > /sys/class/devfreq/bus_dmc/governor just before reboot. 20 out of 20 reboots worked. With devfreq simple_ondemand governor around 50% reboots hung. This could support your thoughts above. Servus, -- Markus > > > With best wishes, > Tobias > -- > 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 > -- 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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