Messages in this thread | | | Date | Fri, 12 Apr 2013 14:09:22 +0200 | From | Nicolas Ferre <> | Subject | Re: [rtc-linux] Re: [PATCH v2 0/5] ARM: at91: fix hanged boot |
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On 04/12/2013 11:33 AM, Johan Hovold : > On Thu, Apr 11, 2013 at 06:54:14PM +0200, Jean-Christophe PLAGNIOL-VILLARD wrote: >> On 17:55 Thu 11 Apr , Johan Hovold wrote: >>> On Mon, Mar 11, 2013 at 07:07:54PM +0100, Johan Hovold wrote: >>>> These patches fix a few severe issues affecting most AT91 SOCs where >>>> boot can hang after a non-general reset, and where the only way to get >>>> the system booting again is to do a general reset -- something which >>>> could require physically removing any backup battery. >>> >>> Have you had time to look at these patches yet, Nicolas? >>> >>> I don't think not having decided on the path forward for DT-support for >>> rtc-at91sam9 needs to be a blocker. The rtt-nodes will be needed in any >>> case. >>> >>> I could respin the series on top of the DT-patch for rtc-at91rm9200, and >>> add interrupt and status-disabled properties to the DT-nodes as well. >> for this this is still a no go >> >> this way too much ugly > > I understand that you prefer fixing every bootloader. I was just making > sure everyone agrees that that is the best solution. > > The two interrupt masks has to be cleared before the kernel enables the > system interrupt; either it needs to be done by the bootloader or by the > at91 arch code. > > The various bootloaders may not know anything about RTT or RTC, but > have all made sure interrupts are disabled before executing the kernel. > That is, they have fulfilled the requirement that interrupts must be > disabled. > > So the trade-off seems to be: Either we fix this once and for all using > the infrastructure already in place in the kernel (DT), or risk further > (apparently) bricked systems as there are bound to be bootloaders that > won't get updated.
Note that I didn't read your patch series yet, so I am not commenting on the implementation.
BUT, from my experience with customers facing this issue, I do thing that we must provide a solution (even in Linux kernel itself).
> [...] > >>>> The problems stem from the fact that the RTC and RTT-peripherals are >>>> powered by backup power (VDDBU) and are not reset on wake-up, user, >>>> watchdog or software reset. Consequently, RTC and RTT-alarms and their >>>> interrupts may be enabled at boot, leading to a system lock-up when an >>>> interrupt arrives on the shared system-interrupt line before the >>>> appropriate handler (e.g. RTC-driver) has been installed. >>>> >>>> The easiest way to trigger this is to simply wake up from an RTC-alarm >>>> on at91sam9g45. The RTC-driver currently does not disable interrupts at >>>> shutdown so even after a clean shut-down the system will always hang >>>> after waking up. >>>> >>>> The first patch fixes this very general case of RTC-wake up after a >>>> clean shutdown in the RTC-driver and is marked for stable as it is >>>> perfectly straight-forward. [ Note that the other, RTT-based, AT91 >>>> RTC-driver already disables its interrupts at shutdown. ] > > And what about this patch? If it's decided that every bootloader needs > to be updated, then perhaps it's better to risk bricked systems also > after a clean shutdown to enforce those updates? Should we then remove > the corresponding disable of interrupts at shutdown from the rtc-at91sam9 > driver by the same logic? > >>>> The more general problem can be triggered, for example, by doing a >>>> user-reset while updating the RTC-time or if an RTC or RTT-alarm goes >>>> off after a non-clean shutdown. >>>> >>>> To fix this I propose that arch-code should mask the relevant interrupts >>>> before enabling the system interrupt at early boot, and this is what >>>> the fifth patch does. To access the RTC-registers I choose to revert a >>>> recent patch that moved the register definitions to drivers/rtc. >>>> >>>> Arguably, the relevant interrupts could also be disabled in bootloaders, >>>> but I suggest fixing it in the kernel once and for all. > > Thanks, > Johan > >
-- Nicolas Ferre
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