[PATCH 1/2] clk: imx: do not sleep if IRQ's are still disabled

Thomas Gleixner
2016-04-27T10:15:00Z

On Wed, 27 Apr 2016, Dong Aisheng wrote:
> On Wed, Apr 27, 2016 at 9:58 AM, Shawn Guo <shawnguo@kernel.org> wrote:
> > On Tue, Apr 26, 2016 at 07:27:03PM +0800, Dong Aisheng wrote:
> >> Shawn,
> >> What's your suggestion?
> >
> > I think this needs more discussion, and I just dropped Stefan's patch
> > from my tree.
> >
> > We need to firstly understand why this is happening. The .prepare hook
> > is defined to be non-atomic context, and so that we call sleep function
> > in there. We did everything right. Why are we getting the warning? If
> > I'm correct, this warning only happens on i.MX7D. Why is that?
> >
>
> Why Stefan's patch works (checking irqs_disabled()) is because during kernel
> time init, the irq is still not enabled. It fixes the issue indirectly.
> See:
> asmlinkage __visible void __init start_kernel(void)
> {
> /*
> * Set up the scheduler prior starting any interrupts (such as the
> * timer interrupt). Full topology setup happens at smp_init()
> * time - but meanwhile we still have a functioning scheduler.
> */
> sched_init();
> .............
> time_init();
> ..............
> WARN(!irqs_disabled(), "Interrupts were enabled early\n");
> early_boot_irqs_disabled = false;
> local_irq_enable();
> }
>
> The issue can only happen when PLL enable causes a schedule during
> imx_clock_init().

Calling a function which might sleep _BEFORE_ kernel_init() is wrong. Don't
try to work around such an issue by doing magic irq_disabled() checks and busy
loops. Fix the call site and be done with it.

Thanks,

tglx