linux-kernel - Re: [PATCH v2 1/1] x86/rtc: Allocate interrupt for platform device

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Date:   Wed, 18 Jan 2017 18:29:10 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org
Subject: Re: [PATCH v2 1/1] x86/rtc: Allocate interrupt for platform device

On Wed, 2017-01-18 at 11:24 +0100, Thomas Gleixner wrote:
> On Tue, 17 Jan 2017, Andy Shevchenko wrote:
> 
> > On Mon, 2017-01-16 at 22:00 +0100, Thomas Gleixner wrote:
> > 
> > > The early callback does not work, but we have one which is invoked
> > > later
> > > on: x86_init.wallclock_init(). That's invoked after the (IO/APIC)
> > > setup has
> > > been completed. See patch below.
> > 
> > Unfortunately it is till too early. Looks like descriptors are not
> > available yet and we still can't get an allocation:
> > 
> > [    0.000000] intel_mid: Failed to allocate RTC interrupt.
> > Disabling
> > RTC
> > 
> > ...
> > 
> > [    0.000000] NR_IRQS:4352 nr_irqs:512 0
> 
> Indeed. Did not think about that we need the irq subsystem up not only
> the
> primary IOAPIC init done.
> 
> Looking deeper it's actually simple. MID already overloads the
> timer_init()
> setup function. So we can just do it there.

Still too early. There is kernel_init() thread which initializes IO-APIC 
IRQs AFAIU. Neither mine, nor your solution would work.

[    0.000000] NR_IRQS:4352 nr_irqs:512 0
[    0.000000] intel_mid: Failed to allocate RTC interrupt. Disabling
RTC
[    0.105359] ENABLING IO-APIC IRQs

I see this one, not sure if it's correct path

kernel_init() ->
 kernel_init_freeable() ->
  smp_prepare_cpus() / native_smp_prepare_cpus() ->
   apic_bsp_setup() ->
    setup_IO_APIC()

So, fixing in rtc.c seems now more reasonable (we may get rid of ugly
#ifdef:s by providing stubs in IOAPIC code).

Another variant is to use just a separate callback on arch_initcall().
It would be closer to current solution.

If you have something better to try, please tell, I would test it.

>  static void __init intel_mid_time_init(void)
>  {
>  	sfi_table_parse(SFI_SIG_MTMR, NULL, NULL, sfi_parse_mtmr);
> 

> +
> +	/* If the platform has an RTC make sure the APIC entry is
> allocated */
> +	if (x86_platform.legacy.rtc)
> +		intel_mid_legacy_rtc_init();

Just in case this should be first call in the function, otherwise it
never been called.

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy