linux-kernel - Re: [PATCH 1/1] ARM: STi: Restore secondary CPU's bringup

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Date:   Wed, 19 Dec 2018 12:14:38 +0000
From:   Patrice CHOTARD <patrice.chotard@...com>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
CC:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] ARM: STi: Restore secondary CPU's bringup

On 12/19/18 12:28 PM, Russell King - ARM Linux wrote:
> On Wed, Dec 19, 2018 at 10:31:35AM +0000, Patrice CHOTARD wrote:
>> Hi Russell
>>
>> On 12/18/18 6:27 PM, Russell King - ARM Linux wrote:
>>> On Tue, Dec 18, 2018 at 05:05:18PM +0000, Patrice CHOTARD wrote:
>>>> Hi Russell
>>>>
>>>> On 12/18/18 4:52 PM, Russell King - ARM Linux wrote:
>>>>> On Tue, Dec 18, 2018 at 03:48:13PM +0100, patrice.chotard@...com wrote:
>>>>>> From: Patrice Chotard <patrice.chotard@...com>
>>>>>>
>>>>>> Due to pen_release and boot_lock removal, secondary CPU's bringup
>>>>>> was broken. Restore CPU's bringup by reworking properly
>>>>>> .smp_prepare_cpus and .smp_boot_secondary STi callbacks.
>>>>>
>>>>> Sorry, maybe I don't understand your commit message, but you seem to be
>>>>> saying that removal of the pen_release and boot_lock broke STi's secondary
>>>>> CPU bring up?  Please clarify, and explain how that happened.
>>>>
>>>> Correct, CPU1 failed to come online.
>>>>
>>>> It seems that writing secondary_startup address at cpu-release-addr in
>>>> .smp_prepare_cpus callback was too early.
>>>>
>>>> Doing it in .smp_boot_secondary callback, insures that secondary_data
>>>> struct is populated in __cpu_up() (stack, pgdir and swapper_pg_dir fields).
>>>
>>> Ah, you're saying that it causes the CPU to jump to secondary_startup
>>> while the boot CPU is in smp_prepare_cpus()?  What triggers the CPU
>>
>> Yes
>>
>>> to jump to the address written to cpu_strt_ptr?  What you're saying
>>> seems to suggest that it's the write to that address, rather than the
>>> IPI that's sent in sti_boot_secondary().
>>
>> At platform startup, an U-Bootrom firmware initialize secondary CPU and
>> make it spinning waiting for a jump address to be written at cpu_strt_ptr.
>>
>> I didn't pay attention to the IPI, you are right IPI is useless, i will
>> remove it.
> 
> Okay, in that case may I suggest an alternative to taking my patch
> which will break this, and then fixing it in a subsequent patch -
> please merge the two patches together so it becomes one "clean up"
> patch which doesn't cause any breakage.
> 
> Thanks.
> 

Ok, agree with your proposal. I will squash our 2 patches.

Thanks

Patrice