From mboxrd@z Thu Jan 1 00:00:00 1970 From: daniel.lezcano@linaro.org (Daniel Lezcano) Date: Thu, 03 Jul 2014 19:44:04 +0200 Subject: timers & suspend In-Reply-To: References: <53B54AC2.5040908@linaro.org> <83fa689b-a06a-4f1c-97cb-f7a7121a0f25@BL2FFO11FD041.protection.gbl> <53B5922A.7020006@linaro.org> Message-ID: <53B59664.3030809@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 07/03/2014 07:30 PM, S?ren Brinkmann wrote: > On Thu, 2014-07-03 at 07:26PM +0200, Daniel Lezcano wrote: >> On 07/03/2014 06:09 PM, S?ren Brinkmann wrote: >>> On Thu, 2014-07-03 at 02:21PM +0200, Daniel Lezcano wrote: >>>> On 06/30/2014 08:39 PM, S?ren Brinkmann wrote: >>>>> Hi, >>>>> >>>>> I'm currently working on suspend for Zynq and try to track down some >>>>> spurious wakes. It looks like the spurious wakes are caused by timers, >>>>> hence I was wondering whether there are any special requirements for >>>>> timer drivers when it comes to suspend support or if I just missed >>>>> something. >>>>> >>>>> Zynq sets the 'IRQCHIP_MASK_ON_SUSPEND' flag, which should mask all >>>>> interrupts but the wake source. Reading through kernel/irq/pm.c >>>>> indicates, that timer interrupts get some special treatment though. >>>>> Therefore I implemented some suspend/resume callbacks for the >>>>> cadence_ttc which disable and clear the timer's interrupts when going >>>>> into suspend. That seems to mitigate the issue quite a bit, but I still >>>>> saw spurious wakes - just a lot less often. >>>>> Digging a little deeper revealed, the spurious wakes are caused by the >>>>> ARM's smp_twd timer now. Given that that driver is probably used by a few >>>>> more ARM platforms, I get the feeling that I'm missing something. >>>> >>>> Do you receive any interrupt from the cadence_ttc ? (/proc/interrupts) >>>> >>>> That's funny because I realize that you cadence ttc timer is never >>>> used as there are the architected timers. The cadence ttc would be >>>> only useful if there were an idle state powering down the smp_twd >>>> timers but it is not the case on this board, IIUC. >>> Yes they are used. They TTC is the only broadcast capable timer for >>> Zynq. In my experience, I can not even boot without it (may have >>> dependencies on CPUidle or something). >> >> Actually the cpuidle driver is wrong. It assumes the state #1 will >> power off the different cores with their architected timers and then >> switch to the broadcast timer. But this one is not needed as we >> don't power down the core with the twd timers, so no need to switch >> to a backup timer device. >> >> The implementation of the DDR self refresh idle state (incoming >> patchset) removes the cpu_pm notifiers + the flag TIMER_STOP. The >> result is 0 interrupts for ttc cadence timer. I removed in the dts >> the cadence ttc and my board booted without problem (it is a zynq >> 702). >> >> Except I missed something, the cadence ttc is actually not used at all. > You mean with your patches, or without? I'd have to check that. I meant with my patches. >>>>> It's probably worth mentioning that the suspend state in Zynq does not >>>>> power off the CPU cores. It just asserts the resets on secondary cores >>>>> and the primary one waits in wfi. >>>> >>>> Why do you need to reset them ? >>> CPU0 is not reset, but all secondary cores are. That is as close to >>> power off as we get and works well with hotplug. >> >> Ok, I was not aware of this approach. Is there any patchset >> available in the net ? > It's in mainline for a while. arch/arm/mach-zynq/platsmp.c defines the > SMP ops. Zynq's cpu_die/kill result in the CPU reset being asserted. And > when the core is plugged in again, it gets deasserted and goes through > the secondary boot path. > That code is a little cleaned up in our vendor tree, but overall it > should be the same functionality wise. Ah, interesting. Thanks for the precision. I was pointing to v3.16-rc3 and I didn't see the upstream xilinx code. So my patchset is now out-dated :( I will look at the code closely. Thanks -- Daniel -- Linaro.org ? Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog