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 00:26:49 -0700
From:	Stefan Agner <stefan@...er.ch>
To:	Shawn Guo <shawnguo@...nel.org>
Cc:	Dong Aisheng <dongas86@...il.com>,
	Lucas Stach <l.stach@...gutronix.de>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	linux-kernel@...r.kernel.org, mingo@...hat.com,
	kernel@...gutronix.de, tglx@...utronix.de,
	linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] clk: imx: do not sleep if IRQ's are still disabled

On 2016-04-27 00:24, Shawn Guo wrote:
> On Wed, Apr 27, 2016 at 10:57:21AM +0800, 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().
>> 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.
> 
> Thanks for the info.  It sounds like that we are fixing the problem in
> the wrong place, i.e. clk_pllv3_prepare().  The function does nothing
> wrong, since the .prepare hook is defined to be one that can sleep.  If
> we see sleep warning in a context calling clk_prepare(), that probably
> means we shouldn't make the function call from that context.
> 

According to the stack trace in the answer to Stephens question the call
comes from imx7d_clocks_init. I doubt we can avoid that those clocks get
enabled there...

--
Stefan