Messages in this thread | | | Date | Mon, 10 Nov 2014 12:58:39 -0800 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH] rtc: Disable EFI rtc for x86 |
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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
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