linux-kernel - Re: [PATCH] rtc: Disable EFI rtc for x86

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Date:	Sun, 9 Nov 2014 18:37:46 +0100
From:	Pali Rohár <pali.rohar@...il.com>
To:	Mark Salter <msalter@...hat.com>
Cc:	Matt Fleming <matt@...sole-pimps.org>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	rtc-linux@...glegroups.com, linux-efi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Matt Fleming <matt.fleming@...el.com>,
	Dave Young <dyoung@...hat.com>
Subject: Re: [PATCH] rtc: Disable EFI rtc for x86

On Friday 03 October 2014 17:01:57 Mark Salter wrote:
> On Fri, 2014-10-03 at 13:32 +0100, Matt Fleming wrote:
> > From: Matt Fleming <matt.fleming@...el.com>
> > 
> > commit da167ad7638759 ("rtc: ia64: allow other architectures
> > to use EFI RTC") inadvertently introduced a regression for
> > x86. We've been careful not to enable the EFI rtc driver
> > for x86 due to the generally buggy implementations of the
> > time-related EFI runtime services.
> > 
> > Previous attempts have been made to us the time EFI
> > services, but all have eventually been reverted due to
> > crashes inside the firmware code.
> > 
> > In fact, since the above commit was merged we've seen
> > reports of crashes on 32-bit tablets,
> > 
> >   https://bugzilla.kernel.org/show_bug.cgi?id=84241#c21
> > 
> > Disable it explicitly for x86 so that we don't give users
> > false hope that this driver will work - it won't, and your
> > machine is likely to crash.
> > 
> > Cc: Mark Salter <msalter@...hat.com>
> > Cc: Dave Young <dyoung@...hat.com>
> > Cc: Alessandro Zummo <a.zummo@...ertech.it>
> > Signed-off-by: Matt Fleming <matt.fleming@...el.com>
> > ---
> 
> Acked-by: Mark Salter <msalter@...hat.com>
> 
> > Unless anyone objects, I'm happy to take this through the
> > EFI tree.
> > 
> >  drivers/rtc/Kconfig | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
> > index a168e96142b9..54ef393b0def 100644
> > --- a/drivers/rtc/Kconfig
> > +++ b/drivers/rtc/Kconfig
> > @@ -806,7 +806,7 @@ config RTC_DRV_DA9063
> > 
> >  config RTC_DRV_EFI
> >  
> >  	tristate "EFI RTC"
> > 
> > -	depends on EFI
> > +	depends on EFI && !X86
> > 
> >  	help
> >  	
> >  	  If you say yes here you will get support for the EFI
> >  	  Real Time Clock.
> 
> --
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Hello,

this patch totally disabled efi rfc driver on x86 machines at 
compile time. But on some x86 machines it working without crash 
and reading from file /sys/class/rtc/rtc*/since_epoch returns 
correct information. So why to disable compiling driver on 
machines where driver working?

-- 
Pali Rohár
pali.rohar@...il.com

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