Tomasz, On Thu, May 15, 2014 at 2:14 PM, Tomasz Figa <tomasz.figa@xxxxxxxxx> wrote: > Hi Chirantan, > > On 15.05.2014 23:07, Chirantan Ekbote wrote: >> The multi core timer and the ARM architected timer are two different >> interfaces to the same underlying hardware timer. This causes some >> strange timing issues when they are both enabled at the same time so >> remove the mct from the device tree and keep only the architected >> timer. > > Huh? I've always thought MCT is a completely separate hardware block > outside of ARM cores, while architected timers are embedded inside the > CPU block in which the ARM cores reside. Could you elaborate on this? Yup. Our thoughts exactly. ...but it appears not to be the case. Chirantan demonstrated this in U-Boot just to prove that it's not some strange kernel interaction in <https://chromium-review.googlesource.com/200035>. I took his patch and tweaked it a little more myself in <https://chromium-review.googlesource.com/200098>. Specifically: * If you stop the MCT, the arch timer stops * If you reset the MCT, the arch timer resets * If you start the MCT again, the arch timer starts again * If you read the MCT and the arch timer, they give the same value. This is apparently the answer to my question at <http://www.spinics.net/lists/linux-samsung-soc/msg29085.html>. Specifically Chirantan found that the big jump in time happened when MCT reset to 0. That made the arch timer code think that there was a wraparound and jump forward in time a lot. Please confirm if you have a system that has MCT and arch timer in front of you. -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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