From mboxrd@z Thu Jan 1 00:00:00 1970 From: "H. Peter Anvin" Subject: Re: [PATCH] rtc: Disable EFI rtc for x86 Date: Mon, 10 Nov 2014 12:58:39 -0800 Message-ID: <546126FF.3070600@zytor.com> References: <1412339576-17972-1-git-send-email-matt@console-pimps.org> <20141109182231.GA29337@pd.tnic> <1415618533.14686.239.camel@mfleming-mobl1.ger.corp.intel.com> <201411101723.49197@pali> <5460EB92.1090501@gmail.com> <20141110170417.GA17286@srcf.ucam.org> <5461220E.20605@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5461220E.20605-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> Sender: linux-efi-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Austin S Hemmelgarn , Matthew Garrett Cc: =?windows-1252?Q?Pali_Roh=E1r?= , Matt Fleming , Borislav Petkov , Mark Salter , Alessandro Zummo , rtc-linux-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org, linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Dave Young List-Id: linux-efi@vger.kernel.org On 11/10/2014 12:37 PM, Austin S Hemmelgarn wrote: > On 2014-11-10 12:04, Matthew Garrett wrote: >> On Mon, Nov 10, 2014 at 11:45:06AM -0500, Austin S Hemmelgarn wrote: >> >>> I agree, without it you need PC CMOS RTC support to access the RTC >>> on most systems, which in turn means that you have to enable the CSM >>> in the EFI firmware, which is annoying cause you can't easily dual >>> boot windows with secure boot when the CSM is enabled. >> >> CMOS RTC support doesn't depend on the CSM. >> > That's really interesting, because with it compiled in, I can't boot on > my EFI based thinkpad laptop without telling EFI to launch the CSM, and > with it compiled out, I can boot fine without the CSM. I'll have to > look further into the options I have set in my kernel build, I may have > changed something else without remembering between booting with and > without the CSM enabled. > It could also be that the non-CSM BIOS somehow remaps the CMOS registers. -hpa