linux-kernel - Re: 4.5-rc4 kernel is failed to bootup on CN6880

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Message-ID: <56CB75F4.9080201@gmail.com>
Date:	Mon, 22 Feb 2016 12:56:20 -0800
From:	David Daney <ddaney.cavm@...il.com>
To:	Yang Shi <yang.shi@...driver.com>
CC:	Aaro Koskinen <aaro.koskinen@...ia.com>, david.daney@...ium.com,
	linux-kernel@...r.kernel.org, linux-mips@...ux-mips.org
Subject: Re: 4.5-rc4 kernel is failed to bootup on CN6880

On 02/22/2016 11:15 AM, Yang Shi wrote:
> On 2/22/2016 4:43 AM, Aaro Koskinen wrote:
>> Hi,
>>
>> On Fri, Feb 19, 2016 at 05:12:41PM -0800, Yang Shi wrote:
>>> I tried to boot 4.5-rc4 kernel on my CN6880 board, but it is failed at
>>> booting up secondary cores. The error is:
>> With v4.5-rc5, EBB6800 is booting fine:
>>
>> [    0.000000] CPU0 revision is: 000d9108 (Cavium Octeon II)
>> [...]
>> [ 2286.273935] SMP: Booting CPU01 (CoreId  1)...
>> [ 2286.278201] CPU1 revision is: 000d9108 (Cavium Octeon II)
>> [...]
>> [ 2287.214953] SMP: Booting CPU31 (CoreId 31)...
>> [ 2287.224668] CPU31 revision is: 000d9108 (Cavium Octeon II)
>> [ 2287.224865] Brought up 32 CPUs
>>
>>> CPU31 revision is: 000d9101 (Cavium Octeon II)
>>> SMP: Booting CPU32 (CoreId 32)...
>>> Secondary boot timeout
>>>
>>> I passed "numcores=32" in kernel commandline since there are 32 cores
>>> ion
>>> CN6880.
>> You shouldn't have CPU32 in that case, the numbering starts from zero.
>> Also the coremask is 32-bit.
>>
>> I can reproduce your issue with CONFIG_NR_CPUS=64. Possibly this code
>> is incorrect for NR_CPUS bigger than 32:
>>
>>          /* The present CPUs get the lowest CPU numbers. */
>>          cpus = 1;
>>          for (id = 0; id < NR_CPUS; id++) {
>>                  if ((id != coreid) && (core_mask & (1 << id))) {
>>                          set_cpu_possible(cpus, true);
>>                          set_cpu_present(cpus, true);
>>
>> What CONFIG_NR_CPUS did you use?
>
> Thanks. I did have 48 NR_CPUS set. It works when I changed it to 32.
>
> I think the problem is core_mask is 32 bit. But when NR_CPUS > 32, in
> "core_mask & (1 << id)" core_mask will be sign extended, then the
> statement will return non-zero all the time.
>

That is correct, and perhaps not coincidentally, the reason I have 
already submitted patches to fix this.

David.


> Yang
>
>>
>> A.
>>
>
>