Messages in this thread | | | From | Bruno Thomsen <> | Date | Tue, 5 May 2020 22:38:13 +0200 | Subject | Re: battery switch-over detection on pcf2127 |
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Hi Rasmus
Den tir. 5. maj 2020 kl. 22.07 skrev Alexandre Belloni <alexandre.belloni@bootlin.com>: > > On 05/05/2020 21:54:47+0200, Rasmus Villemoes wrote: > > Hi Bruno > > > > I just noticed your "rtc: pcf2127: add tamper detection support" > > (03623b4b04) from 5.4. Unfortunately, clearing the BTSE bit breaks a use > > case of ours: > > > > We rely on the battery switch-over detection to distinguish a powerfail > > during boot from a PORESET by the external watchdog (in the latter case, > > the RTC is still powered throughout, meaning there is no battery > > switch-over event). OTOH, we do not use the tamper detection - in fact, > > the TS signal is unconnected on our board. > > > > We're currently still on 4.19, but we will eventually upgrade to a > > kernel containing the above commit. So I was wondering if we could > > figure out a way that would work for both of us - either some CONFIG > > knob, or perhaps something in the device-tree. Any ideas? > > > > Yes, I was working on a patch series last week allowing to read BF. I'm > not sure clearing BTSE is your issue but clearing BF is. > > I'm going to send it tonight, I'll copy you, let me now if that works > for you. You can then read BF using the RTC_VL_READ ioctl. The > RTC_VL_BACKUP_SWITCH flag will be set if a switchover happened. > The RTC_VL_CLR ioctl can be used to clear the flag. > > I think clearing BTSE is still the right thing to do.
I think your use case is valid and it sounds like Alexandre solution will solve it as you just need to know if a battery switch-over has happened not when exactly it happened.
I can help test the patches too. Now without google auto html..
Bruno
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