From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH] ARM: convert arm/arm64 arch timer to use CLKSRC_OF init Date: Tue, 26 Mar 2013 09:56:28 +0000 Message-ID: <201303260956.28784.arnd@arndb.de> References: <1363818875-15978-1-git-send-email-robherring2@gmail.com> <201303252236.23270.arnd@arndb.de> <5150D54D.1070004@linaro.org> Mime-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5150D54D.1070004@linaro.org> Sender: linux-samsung-soc-owner@vger.kernel.org To: John Stultz Cc: Rob Herring , Russell King - ARM Linux , Mark Rutland , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Kukjin Kim , "linux-sh@vger.kernel.org" , Tony Lindgren , Catalin Marinas , Magnus Damm , "rob.herring@calxeda.com" , "linux-samsung-soc@vger.kernel.org" , Simon Horman , Will Deacon , Thomas Gleixner , "linux-omap@vger.kernel.org" List-Id: linux-omap@vger.kernel.org On Monday 25 March 2013, John Stultz wrote: > On 03/25/2013 03:36 PM, Arnd Bergmann wrote: > > On Monday 25 March 2013, Rob Herring wrote: > >> I count integrator-cp, realview, versatile and non-DT VExpress that do > >> this (not surprisingly) and 25 platforms or timer implementations plus > >> arm64 that do sched_clock setup in time_init. What's broken by not > >> moving these earlier? > > timekeeping_init() will leave the persistent_clock_exist variable as "false", > > which is read in rtc_suspend() and timekeeping_inject_sleeptime(). > > Are you mixing up the persistent_clock and sched_clock here? From a > generic stand-point they have different requirements. Ah, sorry about that. I had stumbled over the persistent_clock issue earlier and was confusing the two. > > For all I can tell, you will get a little jitter every time you > > do a suspend in that case. Or perhaps it means the system clock > > will be forwarded by the amount of time spent in suspend twice > > after wakeup, but I'm probably misreading the code for that case. > > No, you shouldn't see timekeeping being incremented twice, we check in > rtc_resume code if the persistent clock is present if so we won't inject > any measured suspend time there. But you're probably right that we're > being a little overly paranoid checking the same value twice. Well, the point is that has_persistent_clock() returns false because it is not yet active when the flag gets set in timekeeping_init(), but when we call read_persistent_clock() in timekeeping_suspend(), it will actually return a non-zero time. > As far as the benefit to the persistent clock: it is just a little > better to use, since we can access it earlier in resume, prior to > interrupts being enabled. So we should see less time error introduced > each suspend. Ok. Arnd