On Wed, Apr 16, 2014 at 09:28:28AM -0700, Sebastian Capella wrote:
> On 15 April 2014 14:18, Pavel Machek <pa...@ucw.cz> wrote:
> > On Tue 2014-04-15 21:54:53, Russell King - ARM Linux wrote:
> >> What I'm basically saying is that I see no reason for ARM to do something
> >> different to what x86 does.
> >>
> >> What is pretty clear to me is that ARM is compatible with x86, which is
> >> compatible with kernel/reboot.c, and it's the hibernate code which is
> >> the odd one out.
> >
> > I'm pretty sure the original code did not return. Anyway, the best
> > solution, given how many platforms are out there, would be to
> >
> > a) document that it should not return
> >
> > b) fix hibernation to handle the returning case, anyway.
>
> Thanks Russell and Pavel!
>
> This sounds fine to me. Any objections?
Here is the i386 code from 2.2.20:
void machine_halt(void)
{
}
void machine_power_off(void)
{
if (acpi_power_off)
acpi_power_off();
}
Both can return. On the other hand, machine_restart() can never return as
the final attempt to perform that action in machine_real_restart is a jump
to 16-bit code.
2.4 kernels then modified it to this:
void machine_halt(void)
{
}
void machine_power_off(void)
{
if (pm_power_off)
pm_power_off();
}
with machine_restart() doing similar to v2.2.
2.6.0 also did the same as 2.4 kernels. 2.6.16 then changed to this:
void machine_restart(char * __unused)
{
machine_shutdown();
machine_emergency_restart();
}
void machine_halt(void)
{
}
void machine_power_off(void)
{
if (pm_power_off) {
machine_shutdown();
pm_power_off();
}
}
which starts adding some extra stuff into the power off hook - but
again, it's a no-op unless the pm_power_off function pointer is
initialised.
Today, it's:
void machine_power_off(void)
{
machine_ops.power_off();
}
which calls native_power_off():
static void native_machine_power_off(void)
{
if (pm_power_off) {
if (!reboot_force)
machine_shutdown();
pm_power_off();
}
/* A fallback in case there is no PM info available */
tboot_shutdown(TB_SHUTDOWN_HALT);
}
and tboot_shutdown():
void tboot_shutdown(u32 shutdown_type)
{
void (*shutdown)(void);
if (!tboot_enabled())
return;
so it's entirely possible today for machine_power_off() on x86 to return.
So... the i386 code has had this "machine_power_off() can return"
behaviour for a significant number of years and persists to this day.
I'd say scrap (a) _unless_ we're going to add while (1) loops to all
the architectures. Alternatively, we could just accept that
machine_power_off() may return and deal with that case (iow, not
crash) in generic code.
--
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improving, and getting towards what was expected from it.
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