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

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Date:	Wed, 27 Apr 2016 12:15:00 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Dong Aisheng <dongas86@...il.com>
cc:	Shawn Guo <shawnguo@...nel.org>,
	Lucas Stach <l.stach@...gutronix.de>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Stefan Agner <stefan@...er.ch>, mingo@...hat.com,
	"kernel@...gutronix.de" <kernel@...gutronix.de>,
	linux-clk@...r.kernel.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/2] clk: imx: do not sleep if IRQ's are still disabled

On Wed, 27 Apr 2016, Dong Aisheng wrote:
> On Wed, Apr 27, 2016 at 9:58 AM, Shawn Guo <shawnguo@...nel.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