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

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Message-ID: <1415618533.14686.239.camel@mfleming-mobl1.ger.corp.intel.com>
Date:	Mon, 10 Nov 2014 11:22:13 +0000
From:	Matt Fleming <matt.fleming@...el.com>
To:	Borislav Petkov <bp@...en8.de>
CC:	Pali Rohár <pali.rohar@...il.com>,
	Mark Salter <msalter@...hat.com>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	<rtc-linux@...glegroups.com>, <linux-efi@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Dave Young <dyoung@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Matthew Garrett <mjg59@...f.ucam.org>
Subject: Re: [PATCH] rtc: Disable EFI rtc for x86

On Sun, 2014-11-09 at 19:22 +0100, Borislav Petkov wrote:
> On Sun, Nov 09, 2014 at 06:37:46PM +0100, Pali Rohár wrote:
> > 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?
> 
> Sounds like we need an efi=rtc_enable knob for people who what to use
> it...

I'm not so sure. By and large, the EFI runtime Time services just don't
work very well on x86. Just because they work sometimes, doesn't
actually mean it's a good idea to use them.

The one scenario where the time services are useful is early on during
boot when we want to get the timezone information. I have vague
recollections of someone working on that.

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