Hi, On 02/11/2022 11:48:04-0700, Guenter Roeck wrote: > Alexandre, > > On Mon, Oct 31, 2022 at 04:07:51PM -0700, Guenter Roeck wrote: > [ ... ] > > > > > > > > On a side note, I tried an alternate implementation by adding a retry into > > > > alarmtimer_suspend(), where it would request a smaller timeout if the > > > > requested timeout failed. I did not pursue/submit this since it seemed > > > > hacky. To solve that problem, I'd rather discuss extending the RTC API > > > > to provide a maximum offset to its users. Such a solution would probably > > > > be desirable, but that it more longer term and would not solve the > > > > immediate problem. > > > > > > Yes, this is what I was aiming for. This is something that is indeed > > > missing in the RTC API and that I already thought about. But indeed, it > > > would be great to have a way to set the alarm range separately from the > > > time keeping range. This would indeed have to be a range relative to the > > > current time. > > > > > > alarmtimer_suspend() can then get the allowed alarm range for the RTC, > > > and set the alarm to max(alarm range, timer value) and loop until the > > > timer has expired. Once we have this API, userspace can do the same. > > > > > > I guess that ultimately, this doesn't help your driver unless you are > > > wanting to wakeup all the chromebooks at least once a day regardless of > > > their EC. > > > > That is a no-go. It would reduce battery lifetime on all Chromebooks, > > including those not affected by the problem (that is, almost all of them). > > > > To implement reporting the maximum supported offset, I'd probably either > > try to identify affected Chromebooks using devicetree information, > > or by sending am alarm request > 24h in the future in the probe function > > and setting the maximum offset just below 24h if that request fails. > > We'd have to discuss the best approach internally. > > > > Either case, that doesn't help with the short term problem that we > > have to solve now and that can be backported to older kernels. It also > > won't help userspace - userspace alarm requests, as Brian has pointed out, > > are separate from limits supported by the RTC hardware. We can not change > > the API for CLOCK_xxx_ALARM to userspace, and doing so would not make > > sense anyway since it works just fine as long as the system isn't > > suspended. Besides, changing alarmtimer_suspend() as you suggest above > > would solve the problem for userspace, so I don't see a need for a > > userspace API/ABI change unless I am missing something. > > > > Would you be open to accepting this patch, with me starting to work > on the necessary infastructure changes as suggested above for a more > comprehensive solution ? > I'll take the patch as-is so you can backport it and have a solution. I'll also work on the alarm range and I'll let you get the series once this is ready so you can test. -- Alexandre Belloni, co-owner and COO, Bootlin Embedded Linux and Kernel engineering https://bootlin.com
