On 15.05.2014 23:44, Kukjin Kim wrote: > On 05/16/14 06:33, Doug Anderson wrote: >> 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. >> > Hi all, > > I need to talk to hardware guy to clarify the issue then I'll let you know. Great, thanks. Having a confirmation from hardware team would be definitely nice. Best regards, Tomasz -- 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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