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

Stefan Agner
2016-04-27T07:26:49Z

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@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().
>> 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