ARM: mxs: warnings on PM resume

[Russell King - ARM Linux]

On Sun, Jun 12, 2016 at 12:27:02PM +0200, Stefan Wahren wrote:
> Hi Rafael,
> 
> > "Rafael J. Wysocki" <rjw at rjwysocki.net> hat am 11. Juni 2016 um 03:42
> > geschrieben:
> > 
> > Interrupts should not be enabled before syscore_resume() is called, but they
> > are, apparently by the platform code.
> 
> sure, but it isn't that simple. I can't reproduce the warning everytime. At
> least i need 5 tries and more to reproduce it.
> 
> I place the following code in the suspend code, before the low level suspend
> code in SRAM gets executed:
> 
> if (!irqs_disabled())
> 	pr_info("IRQs not disabled before suspend\n");
> 
> The info message above only get printed if the warning "Interrupts enabled
> before system core resume." appears.
> 
> After that i dumped all enabled IRQs (at the same code place) from the interrupt
> collector (irqchip) and compared them with cat /proc/interrupts.

This isn't about the state of the interrupt controller.  It's about
the state of the IRQ mask bit in the CPUs CPSR.

irq_disabled() returns true when the I bit in CPSR is set, false
otherwise.

What it's pointing towards is some driver being unreasonable, and
clearing the CPUs CPSR I bit after the core PM code has set it.  Causes
can be using spin_lock_irq()/spin_unlock_irq()/local_irq_enable() etc
inappropriately, rather than using the irqsave/irqrestore versions.

suspend_enter() does this:

        arch_suspend_disable_irqs();
        BUG_ON(!irqs_disabled());

        error = syscore_suspend();

So, we can be sure that if we reach syscore_suspend(), then IRQs were
disabled.

Now, syscore_suspend() calls a set of suspend callbacks, and verifies
that interrupts are not re-enabled after each one.  So, you should be
getting a complaint from the kernel if one of those does trigger, and
these are about the last things that happen before the ->enter
callback is called.  IRQs should be disabled when mxs_suspend_enter()
is entered.

I'm confused by your statement about "the low level suspend code in SRAM
gets executed" - from what I can see in arch/arm/mach-mxs (you said MXS
in the subject), there is no SRAM code that gets executed for S2RAM.
Since you also said MX23, that ties up with mach-mxs, so I can only
conclude that you're using patches on top of mainline which change the
platform suspend code.

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