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

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Date:	Wed, 29 Oct 2014 16:54:22 +0100
From:	Johan Hovold <johan@...nel.org>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Johan Hovold <johan@...nel.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Felipe Balbi <balbi@...com>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	Tony Lindgren <tony@...mide.com>,
	Benoît Cousson <bcousson@...libre.com>,
	Lokesh Vutla <lokeshvutla@...com>, nsekhar@...com,
	t-kristo@...com, j-keerthy@...com, linux-omap@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
	rtc-linux@...glegroups.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 00/20] rtc: omap: fixes and power-off feature

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
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