Am 16.12.2016 um 08:37 schrieb Krzysztof Kozlowski: > On Thu, Dec 15, 2016 at 04:52:58PM -0800, Doug Anderson wrote: >>> [ I added Arjun to Cc:, maybe he can help in explaining this issue >>> (unfortunately Inderpal's email is no longer working). ] >>> >>> Please also note that on Exynos5422/5800 SoCs the same ARM rail >>> voltage is used for 1.9 GHz & 2.0 GHz OPPs as for the 1.8 GHz one. >>> IOW if the problem exists it is already present in the mainline >>> kernel. >> >> Interesting. In the ChromeOS tree I see significantly higher voltages >> needed... Note that one might naively look at >> <https://chromium.googlesource.com/chromiumos/third_party/kernel/+/chromeos-3.8/drivers/cpufreq/exynos5420-cpufreq.c#178>. >> >> 1362500, /* L0 2100 */ >> 1312500, /* L1 2000 */ >> >> ..but, amazingly enough those voltages aren't used at all. Surprise! >> >> I believe that the above numbers are actually not used and the ASV >> numbers are used instead. See >> <https://chromium.googlesource.com/chromiumos/third_party/kernel/+/chromeos-3.8/arch/arm/mach-exynos/include/mach/asv-exynos542x.h#452> >> >> { 2100000, >> 1350000, 1350000, 1350000, 1350000, 1350000, >> 1337500, 1325000, 1312500, 1300000, 1287500, >> 1275000, 1262500, 1250000, 1237500 }, >> >> I believe that interpretation there is: some bins of the CPU can run >> at 2.1 GHz just fine at 1.25 V but others need up to 1.35V. > > That is definitely the case. One could just look at vendors ASV table > (for 1.9 GHz): > { 1900000, 1300000, 1287500, 1262500, 1237500, 1225000, 1212500, > 1200000, 1187500, 1175000, 1162500, 1150000, > 1137500, 1125000, 1112500, 1112500}, > > The theoretical difference is up to 1.875V! From my experiments I saw > BIN1 chips which should be the same... but some working on 1.2V, some on > 1.225V (@1.9 GHz). I didn't see any requiring higher voltages but that > does not mean that there aren't such... > >> ...so if you're running at 2.1 GHz at 1.25V then perhaps you're just >> running on a CPU from a nice bin? I've been running the proposed frequency/voltage combinations without any stability problems on my XU4, XU3 and even XU3-lite ( I did not delete the nodes on XU3-lite dts) with make -j8 kernel and ssvb-cpuburn. The chips are poorly cooled, especially the XU4 and quickly step down. > > Would be nice to see a dump of PKG_ID and AUX_INFO chipid registers > along with name of tested board. Because the "Tested on XU3" is not > sufficient. If you point me to how to read these values out, I will publish them. > > Best regards, > Krzysztof -- Markus Reichl -- 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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