Re: [PATCH] rtc: Disable EFI rtc for x86

From: Austin S Hemmelgarn
Date: Mon Nov 10 2014 - 11:45:25 EST


On 2014-11-10 11:23, Pali RohÃr wrote:
On Monday 10 November 2014 12:22:13 Matt Fleming wrote:
On Sun, 2014-11-09 at 19:22 +0100, Borislav Petkov wrote:
On Sun, Nov 09, 2014 at 06:37:46PM +0100, Pali RohÃr 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.

On laptop Dell Latitude E6440 with 64bit kernel 3.17-rc6 (where
was rtc-efi.ko enabled at compile time for x86) it working fine
without crash. So I think that other Dell machines could work
too.

I can also confirm that it works correctly on a number of ASUS and ASrock desktop motherboards with the most recent BIOS updates, and on a Lenovo Thinkpad L540. I can however confirm that it DOES NOT work however on an Acer Aspire V5-131 system, though I had never updated the BIOS on that one, so it may work correctly with a newer BIOS version.
Maybe problems which were reported are only specific for 32bit
UEFI? Or 32bit kernels?

And I think that if I know that efi time service working on
machine, I should be able to use it with mainline kernel (without
hacking Kconfig to enable it and so...).

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.

Attachment: smime.p7s
Description: S/MIME Cryptographic Signature