From: kgene.kim@samsung.com (Kukjin Kim) Date: Fri, 16 May 2014 06:44:02 +0900 Subject: [PATCH] arm: dts: exynos5: Remove multi core timer In-Reply-To: References: <1400188079-21832-1-git-send-email-chirantan@chromium.org> <53752E25.9060604@gmail.com> Message-ID: <53753522.30107@samsung.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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. Thanks, Kukjin