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

[Dong Aisheng]

On Wed, Apr 27, 2016 at 3:34 PM, Stefan Agner <stefan at agner.ch> wrote:
> On 2016-04-26 19:57, Dong Aisheng wrote:
>> On Wed, Apr 27, 2016 at 9:58 AM, Shawn Guo <shawnguo at 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.
>
> Oh ok, it does make sense to enable as few clocks as possible.
>
> However, even if we do not enable lots of clocks at that time, and this
> helps to avoid the problem for now, it could still be that
> someone/something requests a clock early during boot, leading to a PLL
> enable... Shouldn't we make sure that those base clocks can be enabled
> even during early boot..?
>

The point as Shawn pointed is that we even shouldn't call clk_prepare_enable
at that time.
So we may first try to eliminate those callings in imx7d_clocks_init.

> --
> Stefan

Regards
Dong Aisheng