From mboxrd@z Thu Jan 1 00:00:00 1970 From: tomasz.figa@gmail.com (Tomasz Figa) Date: Thu, 15 May 2014 23:44:49 +0200 Subject: [PATCH] arm: dts: exynos5: Remove multi core timer In-Reply-To: <53753522.30107@samsung.com> References: <1400188079-21832-1-git-send-email-chirantan@chromium.org> <53752E25.9060604@gmail.com> <53753522.30107@samsung.com> Message-ID: <53753551.2040808@gmail.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 >> 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 >> . I took his patch >> and tweaked it a little more myself in >> . >> >> 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 >> . >> 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