linux-kernel - Re: AMR: sun7i: CPU hotplug support?

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Message-ID: <54609C82.9020103@arm.com>
Date:	Mon, 10 Nov 2014 11:07:46 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Jan Kiszka <jan.kiszka@....de>
CC:	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-sunxi@...glegroups.com" <linux-sunxi@...glegroups.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: AMR: sun7i: CPU hotplug support?

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On 10/11/14 10:33, Jan Kiszka wrote:
> On 2014-11-10 10:52, Marc Zyngier wrote:
>> On 10/11/14 09:36, Jan Kiszka wrote:
>>> On 2014-11-10 10:17, Marc Zyngier wrote:
>>>> On 10/11/14 08:25, Jan Kiszka wrote:
>>>>> On 2014-11-10 07:03, Jan Kiszka wrote:
>>>>>> On 2014-11-10 00:17, Maxime Ripard wrote:
>>>>>>> Hi Jan,
>>>>>>> 
>>>>>>> On Sun, Nov 09, 2014 at 08:35:49PM +0100, Jan Kiszka 
>>>>>>> wrote:
>>>>>>>> did anyone already happen to look into enabling CPU 
>>>>>>>> hotplug for the Allwinner A20 in upstream? I'm
>>>>>>>> currently running the sunxi-next branch on Banana Pi,
>>>>>>>> and echo 0 > .../cpu1/online just hangs the system.
>>>>>>>> The old 3.4 LeMaker kernel works fine in this regard.
>>>>>>>> I can try to look into details and port things over,
>>>>>>>> just want to avoid duplicate efforts.
>>>>>>> 
>>>>>>> Having hotplug support would indeed be very welcome.
>>>>>>> 
>>>>>>> However, it should be done in u-boot, through PSCI, and
>>>>>>> not in the kernel itself.
>>>>>>> 
>>>>>>> As far as I'm aware, no one worked actively on it,
>>>>>>> beside some WIP commit from Marc a while ago: 
>>>>>>> https://git.kernel.org/cgit/linux/kernel/git/maz/u-boot.git/commit/?h=wip/psci&id=45379c0f9cf812f0f62722f4015ec907fa5dc144
>>>>>>
>>>>>>
>>>>>>>
>>>>
>>>>>>>
>>
>>>>>>> 
OK - I guess I will need a little guidance in then: Is there a good
>>>>>> reference board to study and to derive from? And maybe
>>>>>> also: What is missing or not working in that u-boot
>>>>>> branch? If I get this interface right, I just takes some
>>>>>> device tree bits to enable this for the kernel afterward,
>>>>>> correct?
>>>>> 
>>>>> Started to play with that patch in naive ways: CPU0 locks
>>>>> up when offlining CPU1 - unless I disable the FIQ signal
>>>>> from CPU1. Then it "works", both offlining and onlining
>>>>> again. However, I suspect that this only parks CPU1 in wfi
>>>>> and does not do anything interesting to it.
>>>> 
>>>> Here's how this is supposed to work: - CPU1 sends a FIQ to
>>>> CPU0, bringing it into secure mode. - CPU0 then kills CPU1 by
>>>> doing the magic incantations on the power controller
>>>> 
>>>> What is missing here is all the cache cleaning before
>>>> signalling CPU0. If you add that, things should look a lot
>>>> better (patches welcome).
>> 
>>> Unsure about this, or maybe this was too simplistic: I added
>>> calls to u-boot's flush_dcache_all and invalidate_icache_all
>>> (right after disabling the cache, just like the vendor kernel
>>> does), but CPU0 still locks up. I suspect there is still a bug
>>> in the FIQ handling. There is also a suspicious single "@"
>>> printed on the console. I'll play with the FIQ handler a bit.
>> 
>> The '@' is just my own debug stuff, and might be causing issues
>> too.
>> 
>> Now, you have to realise that by the time you call into this
>> code, u-boot itself is long gone. Only the tiny bit of code
>> dealing with PSCI still lives in a bank of static, secure memory.
>> So calling into u-boot for anything is doomed. You need to
>> actually put the code inside the PSCI backend.
> 
> OK - seems like quite a bit of code needs to be pulled over...
> 
> Meanwhile I'm still starring at psci_fiq_enter: ... movw	r8,
> #(GICC_BASE & 0xffff) movt	r8, #(GICC_BASE >> 16) ldr	r9, [r8,
> #GICC_IAR] movw	r10, #0x3ff movt	r10, #0 cmp	r9, r10 bne	out1 movw
> r10, #0x3fe cmp	r9, r10 bne	out1 ...
> 
> How can GICC_IAR be 0x3ff and 0x3fe at the same time? These tests
> seems bogus. What was the actual intention here?

Yup, that looks like a massive brain fart. These two 'bne' should
really be 'beq's... You want to get out if you either read that there
is no interrupt (0x3ff) or an interrupt for non-secure (0x3fe).

	M.
- -- 
Jazz is not dead. It just smells funny...
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