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Date:	Wed, 27 Apr 2016 10:57:21 +0800
From:	Dong Aisheng <dongas86@...il.com>
To:	Shawn Guo <shawnguo@...nel.org>
Cc:	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>,
	tglx@...utronix.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, 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().
Not all PLL has this issue.
The issue happens on MX7D pll_audio_main_clk/pll_video_main_clk
which requires more delay time and cause usleep.
Because clk framework does not support MX7D clock types (operation requires
parents on), we simply enable all clocks in imx7d_clocks_init().

If apply my this patch series:
https://lkml.org/lkml/2016/4/20/199
The issue can also be gone.

Regards
Dong Aisheng

> Shawn

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