Messages in this thread | | | Date | Wed, 21 Sep 2016 22:09:28 +0200 | From | Alexandre Belloni <> | Subject | Re: [PATCH v4 2/2] rtc-cmos: Restore alarm after resume |
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On 20/09/2016 at 01:12:44 +0200, Gabriele Mazzotta wrote : > Some platform firmware may interfere with the RTC alarm over suspend, > resulting in the kernel and hardware having different ideas about system > state but also potentially causing problems with firmware that assumes the > OS will clean this case up. This patch restores the RTC alarm on resume > to ensure that kernel and hardware are in sync. > > The case we've seen is Intel Rapid Start, which is a firmware-mediated > feature that automatically transitions systems from suspend-to-RAM to > suspend-to-disk without OS involvement. It does this by setting the RTC > alarm and a flag that indicates that on wake it should perform the > transition rather than re-starting the OS. However, if the OS has set a > wakeup alarm that would wake the machine earlier, it refuses to overwrite > it and allows the system to wake instead. > > This fails in the following situation: > > 1) User configures Intel Rapid Start to transition after (say) 15 > minutes > 2) User suspends to RAM. Firmware sets the wakeup alarm for 15 minutes > in the future > 3) User resumes after 5 minutes. Firmware does not reset the alarm, and > as such it is still set for 10 minutes in the future > 4) User suspends after 5 minutes. Firmware notices that the alarm is set > for 5 minutes in the future, which is less than the 15 minute transition > threshold. It therefore assumes that the user wants the machine to wake > in 5 minutes > 5) System resumes after 5 minutes > > The worst case scenario here is that the user may have put the system in a > bag between (4) and (5), resulting in it running in a confined space and > potentially overheating. This seems reasonably important. The Rapid > Start support code got added in 3.11, but it can be configured in the > firmware regardless of kernel support. > > Signed-off-by: Gabriele Mazzotta <gabriele.mzt@gmail.com> > --- > drivers/rtc/rtc-cmos.c | 23 +++++++++++++++++++++++ > 1 file changed, 23 insertions(+) > Applied, thanks.
-- Alexandre Belloni, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com
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