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

From: Nikita Yushchenko <nyushchenko@dev.rtsoft.ru>
To: Vladimir Murzin <vladimir.murzin@arm.com>
Cc: Russell King - ARM Linux <linux@arm.linux.org.uk>,
	kuznetsovg@dev.rtsoft.ru, Ian Campbell <ian.campbell@citrix.com>,
	Mason <slash.tmp@free.fr>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Will Deacon <will.deacon@arm.com>,
	Paul Kocialkowski <contact@paulk.fr>,
	linux-kernel@vger.kernel.org,
	Masahiro Yamada <yamada.m@jp.panasonic.com>,
	Pavel Machek <pavel@ucw.cz>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case
Date: Mon, 23 Nov 2015 15:47:34 +0300	[thread overview]
Message-ID: <56530AE6.2060407@dev.rtsoft.ru> (raw)
In-Reply-To: <5653099A.7020604@dev.rtsoft.ru>

>>>>> While running an imx6s boasrd, I got following message in boot log:
>>>>>
>>>>> [    0.032414] CPU1: failed to boot: -38
>>>>>
>>>>> This looked strange: imx6s is singe-core and kernel perfectly knows
>>>>> that. However, for some reason it tries to initialize CPU 1?
>>>>>
>>>>> I found this to be caused by
>>>>> - CONFIG_SMP_ON_UP successfully detects that system is single core,
>>>>> - this causes is_smp() to return false,
>>>>> - this causes setup_arch() to skip smp_init_cpus() call,
>>>>> - this skips board-specific code that sets cpu_possible mask.
>>>>
>>>> Right, so you should end up with the possible and present masks
>>>> containing just one CPU, which should prevent the kernel trying to
>>>> bring any secondary CPUs online.
>>>
>>> Kernel that is running here still tries to init CPU 1 for some reason.
>>
>> I *guess* cpus node [1] in your dts has more than one cpu entry, could
>> you check please?
> 
> Indeed looks so:
> 
> # ls /proc/device-tree/cpus
> #address-cells  #size-cells  cpu@0  cpu@1  name
> 
> But my custom device tree just includes imx6dl.dtsi
> 
> So it is imx6dl.dtsi in linux-imx tree broken?..

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 :(