Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case

From	Nikita Yushchenko <nyushchenko@dev.rtsoft.ru>
Newsgroups	linux.kernel
Subject	Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case
Date	2015-11-24 16:00 +0100
Message-ID	<qynez-130-33@gated-at.bofh.it> (permalink)
References	(2 earlier) <qxY6t-1yt-1@gated-at.bofh.it> <qxYzw-1JL-9@gated-at.bofh.it> <qxYJc-1N0-7@gated-at.bofh.it> <qxYJc-1N0-9@gated-at.bofh.it> <qxZ2y-29g-13@gated-at.bofh.it>
Organization	RTSoft Software Development Center

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>> Just booted mainline...  unline linux-imx, it does not try to init cpu1.
>>
>> However, imx6dl.dtsi from mainline also has both cpu@0 and cpu@1
>>
>> So missing piece in linux-imx is elsewhere :(
> 
> It works as you mentioned - and it relies upon the code you tried to
> modify.
> 
> The early boot code detects that the boot CPU is not SMP capable, so
> through SMP_ON_UP, it "turns off" SMP support by fixing up the code
> and making is_smp() return false.
> 
> This prevents smp_init_cpus() being called, which in turn prevents
> imx_smp_init_cpus() executing, which prevents the CPU possible mask
> including any CPU but the boot CPU.
> 
> As only the boot CPU is possible, this prevents the SMP code trying
> to bring any secondary CPUs online.

I'm still trying to understand what is going on, and my printk()s show
that this is not entirely true.

When smp_init() is entered on mainline om imx6s, cpu_possible_mask and
cpu_present_mask both contain two cpus. These get initialized in
arm_dt_init_cpu_maps() and stay unmodified since then.

But cpu_online() returns 1 for cpu0 and 0 from cpu1 - thus it is
cpu_online() check, not possible_mask or present_mask, that prevents
cpu1 initialization attempt.

Not sure I understand logic behind this. With the current code,
resulting cpu_possible_mask depends on CONFIG_SMP_ON_UP:
- if it is set, cpu_possible_mask contains (0 1), as initialized in
arm_dt_init_cpu_maps()
- if it is not set, cpu_possible_mask contains (0), since
imx_smp_init_cpus() removes 1 from there.

This does not seem to be intended difference.




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Thread

[RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case nyushchenko@dev.rtsoft.ru - 2015-11-23 13:00 +0100
  Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Nikita Yushchenko <nyushchenko@dev.rtsoft.ru> - 2015-11-23 13:10 +0100
    Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-11-23 13:20 +0100
      Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Nikita Yushchenko <nyushchenko@dev.rtsoft.ru> - 2015-11-23 13:50 +0100
    Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-11-23 13:20 +0100
    Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Vladimir Murzin <vladimir.murzin@arm.com> - 2015-11-23 13:40 +0100
      Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Nikita Yushchenko <nyushchenko@dev.rtsoft.ru> - 2015-11-23 13:50 +0100
        Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-11-23 14:10 +0100
          Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Nikita Yushchenko <nyushchenko@dev.rtsoft.ru> - 2015-11-24 16:00 +0100
            Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Nikita Yushchenko <nyushchenko@dev.rtsoft.ru> - 2015-11-24 16:10 +0100
              Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Nikita Yushchenko <nyushchenko@dev.rtsoft.ru> - 2015-11-24 16:30 +0100
            Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-11-24 16:40 +0100
              Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Nikita Yushchenko <nyushchenko@dev.rtsoft.ru> - 2015-11-28 12:20 +0100
                Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Nikita Yushchenko <nyushchenko@dev.rtsoft.ru> - 2015-11-30 09:30 +0100
      Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Nikita Yushchenko <nyushchenko@dev.rtsoft.ru> - 2015-11-23 13:50 +0100
  Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-11-23 13:10 +0100

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