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? 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. Best regards, Krzysztof -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
