From mboxrd@z Thu Jan 1 00:00:00 1970 From: t-kristo@ti.com (Tero Kristo) Date: Thu, 16 Jul 2015 15:03:50 +0300 Subject: [PATCH 0/3] ARM: OMAP2+: hwmod: RTC: Add lock and unlock hooks In-Reply-To: References: <1433928386-24891-1-git-send-email-lokeshvutla@ti.com> <55A4DFEF.6040005@ti.com> <55A52208.5060302@ti.com> <55A758A3.2070108@ti.com> Message-ID: <55A79DA6.4070206@ti.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 07/16/2015 01:13 PM, Paul Walmsley wrote: > On Thu, 16 Jul 2015, Tero Kristo wrote: > >> On 07/16/2015 03:15 AM, Paul Walmsley wrote: >>> On Tue, 14 Jul 2015, Tero Kristo wrote: >>> >>>> On 07/14/2015 01:09 PM, Lokesh Vutla wrote: >>>>> Hi, >>>>> On Wednesday 10 June 2015 02:56 PM, Lokesh Vutla wrote: >>>>>> Some IP blocks like RTC, needs an additional unlocking mechanism for >>>>>> writing to its registers. This patch adds optional lock and unlock >>>>>> function pointers to the IP block's hwmod data which gets executed >>>>>> before and after writing into IP sysconfig register. >>>>>> And also hook lock and unlock functions to AMx3xx, DRA7 RTC hwmod >>>>>> data, >>>>>> so that sysconfig registers are updated properly. >>>>> ping on this series. >>>>> >>>>> Thanks and regards, >>>>> Lokesh >>>> >>> >>> [...] >>> >>>> It is also racy, as there is no locking in place to avoid concurrent >>>> access to >>>> the lock/unlock registers across hwmod+driver. >>> >>> I don't see the race. Where is it? >> >> See drivers/rtc/rtc-omap.c, am3352_rtc_unlock and am3352_rtc_lock. >> >> That code is accessing the exact same registers. > > I guess my question is, when is it possible that code could race with the > hwmod code for the same device? Hmm yea I think you are right, this only gets potentially called within pm_runtime_get/put_sync for RTC. The current sequence is highly inefficient though, as we are doing multiple lock/unlock operations to the RTC from multiple sources. See following rtcwake trace on am43xx-gp-evm as an example. / # rtcwake -s 4 -m mem [ 7.425322] am3352_rtc_unlock [ 7.428330] am3352_rtc_lock [ 7.431139] am3352_rtc_unlock [ 7.434116] am3352_rtc_lock wakeup from "mem" at Sat Jan 1 00:00:11 2000 [ 7.448549] PM: Syncing filesystems ... done. [ 7.455425] Freezing user space processes ... (elapsed 0.001 seconds) done. [ 7.463738] Freezing remaining freezable tasks ... (elapsed 0.001 seconds) do ne. [ 7.472532] Suspending console(s) (use no_console_suspend to debug) [ 7.481878] am3352_rtc_unlock [ 7.481889] am3352_rtc_lock [ 7.482307] PM: suspend of devices complete after 2.713 msecs [ 7.483479] PM: late suspend of devices complete after 1.153 msecs [ 7.484727] omap_hwmod_rtc_unlock [ 7.484733] omap_hwmod_rtc_lock [ 7.485182] PM: noirq suspend of devices complete after 1.685 msecs [ 7.485190] Disabling non-boot CPUs ... [ 7.485199] PM: Successfully put all powerdomains to target state [ 7.485199] PM: Wakeup source RTC Alarm [ 7.499853] PM: noirq resume of devices complete after 14.558 msecs [ 7.500047] am3352_rtc_unlock [ 7.500052] am3352_rtc_lock [ 7.500123] am3352_rtc_unlock [ 7.500128] am3352_rtc_lock [ 7.501019] PM: early resume of devices complete after 0.809 msecs [ 7.501464] am3352_rtc_unlock [ 7.501472] am3352_rtc_lock [ 7.558046] PM: resume of devices complete after 57.007 msecs [ 7.638807] Restarting tasks ... done. [ 7.643173] am3352_rtc_unlock [ 7.646162] am3352_rtc_lock But, I guess this is for some interested party to optimize if needed, and it is mostly an issue with the RTC driver itself. -Tero