[PATCH 2/3] corenet: Support gpio power/reset for corenet

[Scott Wood]

On 09/10/2016 05:05 PM, Andy Fleming wrote:
> 
> 
> On Tuesday, September 6, 2016, Scott Wood <scott.wood at nxp.com
> <mailto:scott.wood at nxp.com>> wrote:
> 
>     On 09/06/2016 02:12 PM, Andy Fleming wrote:
>     > Boards can implement power and reset functionality over gpio using
>     > these drivers:
>     >   drivers/power/reset/gpio-poweroff.c
>     >   drivers/power/reset/gpio-restart.c
>     >
>     > While not all corenet boards use gpio for power/reset, this
>     > support can be added without interfering with boards that do not
>     > use this functionality.
>     >
>     > If a board's device tree has the related nodes, they are now probed.
>     > Also, gpio-poweroff uses the global pm_power_off callback to implement
>     > the shutdown. However, pm_power_off was not invoked when the kernel
>     > halted, although that is usually the desired behavior. If the board
>     > provides gpio power and reset support, it is reasonable to assume that
>     > halting should also power down the system, unless it has chosen to
>     > pass those calls on to hypervisor.
> 
>     Halt and poweroff are not the same thing.  If userspace requests a
>     poweroff, then kernel_power_off() will call machine_power_off() which
>     will call pm_power_off().
> 
>     Why do we need anything corenet-specific here?
> 
> 
> 
>     We don't, but then the board will halt instead of power off when you
>     type shutdown -h now.

Isn't that what it's supposed to do?  If you want poweroff then ask for
poweroff.

>     Or if you type poweroff without a high enough
>     run level, apparently.

Hmm?

In any case, run levels have nothing to do with the kernel.  The kernel
implements LINUX_REBOOT_CMD_HALT and LINUX_REBOOT_CMD_POWER_OFF, and
they should do what they're advertised to do.

>     I'm amenable to removing the halt code, but
>     there are concerns that this will cause the systems to behave
>     unintentionally as intended, in that most systems that users
>     interact with shut down when you call shutdown -h now. There may be
>     scripts that depend on that behavior (or at least assume it).

When did the behavior you're seeking ever exist?

>     I don't see any other platforms doing this.  How do the nodes get probed
>     for them?
> 
> 
>     The answer is I don't know, but this is a common issue with adding
>     new devices to the device tree in embedded powerpc. The only other
>     platforms which have gpio-poweroff nodes in their trees are in
>     arch/arm, and none of those platforms call the probing
>     function of_platform_bus_probe. I suspect they either probe every
>     root node, or they somehow construct the match_id. As noted in the
>     above-referenced commit, putting the nodes under the gpio bus does
>     not cause them to get probed. This seemed like the best way under
>     the current corenet code.

Well, let's figure out what it is that PPC should be doing to have
things work the way it does on ARM.

-Scott