linux-kernel - Re: [REGRESSION] 41c7f74 rtc: Disable the alarm in the hardware (v2)

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Message-ID: <1077642371.409848.1386924111059.JavaMail.sas1@[172.29.241.231]>
Date:	Fri, 13 Dec 2013 09:41:51 +0100
From:	Brecht Machiels <brecht@...6581.org>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Borislav Petkov <bp@...en8.de>, <linux-kernel@...r.kernel.org>
Subject: Re: [REGRESSION] 41c7f74 rtc: Disable the alarm in the hardware
 (v2)

---- On Thu, 12 Dec 2013 22:16:55 +0100 John Stultz<john.stultz@...aro.org> wrote ---- 

 > On 12/12/2013 11:39 AM, John Stultz wrote: 
 > > On 12/05/2013 03:51 AM, Brecht Machiels wrote: 
 > >> On Mon, 02 Dec 2013 22:19:58 +0100, Borislav Petkov wrote: 
 > >> 
 > >>> On Mon, Dec 02, 2013 at 12:47:17PM -0800, John Stultz wrote: 
 > >>>> Ok, sorry about this. I've been hoping we'd get some better insight 
 > >>>> into what's actually happening on these strange BIOSes where disabling 
 > >>>> the irq seems to cause it to scream (powering the system back on when 
 > >>>> its shutdown), in the hopes of having a proper workaround. But despite 
 > >>>> Borislav's efforts, he didn't seem to be able to root cause the issue. 
 > >>> Right, this bug is too nasty - you could generate good random numbers 
 > >>> just from how the hardware behaves. :) And I've been trying to make 
 > >>> sense of what happens but I failed, as you know. :( 
 > >>> 
 > >>> I consider it a huge waste of time and efforts having to deal with such 
 > >>> b0rked hardware instead of throwing it out of the window into the poring 
 > >>> rain while it is still powered. 
 > >>> 
 > >>>> Borislav, could you double check this patch still works on your 
 > >>>> hardware as well? 
 > >>> Well, we have the patch in SLES11: 
 > >>> 
 > >>> http://kernel.opensuse.org/cgit/kernel/commit/?h=SLE11- 
 > >> SP3&id=835398eb94dca7d55acd1a2628372e602ae3252a 
 > >>> and it passed testing. 
 > >>> 
 > >>> From what I see below, your version is equivalent to the one above with 
 > >>> the logic reversed so it should work. I'll still try to get that 
 > >>> affected box and run your version on it but it'll take a while. 
 > >> Hello John and Boris, 
 > >> 
 > >> Thank you for your quick response. And no need for an apology, I can  
 > >> understand your frustration with the way some hardware behaves. 
 > >> 
 > >> I ran with John's patch for a couple of days, and it seems to work.  
 > >> Curiously, the laptop did spontaneously boot the first time that I shut  
 > >> it down with the patched kernel. I have no conclusive explanation for  
 > >> this, but I have noticed that a manual power down is necessary after  
 > >> booting with an unpatched kernel. Simply rebooting with a patched kernel  
 > >> is not enough to stop the spontaneous boots. As far as I can remember, I  
 > >> went directly from my custom kernel (with the v2 patch reverted) to a  
 > >> kernel with your patch applied, so I'm not 100% convinced everything is  
 > >> all right. I should say that I did experience some spontaneous boots when  
 > >> running only Windows XP in the past, so there may be occasions where  
 > >> drivers might not be able to help at all. 
 > > Yea. It seems almost like the RTC_AIE bit is inverted in the hardware or 
 > > something. 
 > > 
 > >> Thankfully, after other shutdowns/hibernates (about 6 in total) the  
 > >> laptop never booted spontaneously. 
 > >> 
 > >> As for killing alarm functionality on the affected systems, I did some  
 > >> quick tests. With the patched kernel, I can set the RTC alarm by echoing  
 > >> to /sys/class/rtc/rtc0/wakealarm, and the machine will boot at the  
 > >> specified time. I have also tried setting the RTC alarm, and then  
 > >> disabling it again by echoing '0' to /sys/class/rtc/rtc0/wakealarm. While  
 > >> this sets the alrm_time to five minutes in the future, alarm_IRQ is set  
 > >> to 'no' and the machine does *not* boot spontaneously 5 minutes after  
 > >> shutting down. So, all seems well, as far as I can see. Unfortunately, I  
 > >> don't know enough about the RTC driver to draw any conclusions from this. 
 > > Ok. Sounds like the patch works fairly well then. I'll go ahead and 
 > > queue it for 3.14 and -stable. 
 > Brecht: Is it OK if I add to the patch: 
 >  Tested-by: Brecht Machiels <brecht@...6581.org> 

Sure.

Thanks,
Brecht

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