Hi Tobias, Am Montag, 21. November 2016, 16:16:24 schrieb Tobias Jakobi: > Hello Markus, > > > Markus Reichl wrote: > > 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. > thanks for the tests. I assume by 'reboots hung' you mean that the boot > process doesn't even reach u-boot? Yes, in these cases u-boot does not appear on the U3. -- Markus > > - Tobias > > > > 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
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