Re: [PATCH v2 00/20] rtc: omap: fixes and power-off feature

Johan Hovold
2014-10-29T15:57:30Z

On Wed, Oct 29, 2014 at 08:36:41AM -0700, Guenter Roeck wrote:
> On Wed, Oct 29, 2014 at 02:35:26PM +0100, Johan Hovold wrote:
> > On Wed, Oct 29, 2014 at 06:20:40AM -0700, Guenter Roeck wrote:
> > > On 10/29/2014 05:34 AM, Johan Hovold wrote:

> > > > And what about any power-off latencies? Should this always be dealt with
> > > > in the power-off handler?
> > > >
> > > > Again, if it's predictable and high, as in the OMAP RTC case, it should
> > > > go in the handler. But what if it's just normal bus latencies
> > > > (peripheral busses, i2c, or whatever people may come up with)?
> > > >
> > > > Should there always be a short delay before calling the next handler?
> > >
> > > That delay would depend on the individual power-off handler, so I think
> > > the current implementation works just fine (where power-off handlers
> > > implement the delay).
> >
> > Some don't, and could possibly unknowingly have been relying on the fact
> > that they could return to user space and be powered off at some later
> > time. With systemd that would have caused a panic.
>
> Agreed, but there are two cases to consider: What should be the delay
> before the next power-off handler is called, and what should the system
> do if all power-off handlers fail (or if there are none). The current
> behavior isn't exactly well defined. Ok, with systemd that results in
> a crash, but I am not really sure if one can or should blame systemd
> for that. The discussion about systemd and its philosophy should not
> cloud the fact that power-off behavior isn't exactly well defined.

Sounds like we pretty much agree. See my response to your last mail.

> > Also consider generic power-off handlers such as gpio-poweroff. It
> > currently hard-codes a three-second delay but the actual delay would
> > really be board specific.
> >
> A configurable delay would address that. The actually required delay
> could be provided in platform data or as devicetree property.

Yep, see mail mentioned above.

Johan