linux-kernel - Re: Allowing reset controllers before SMP initialization (on ARM)?

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Date:	Thu, 16 Apr 2015 11:42:08 +0200
From:	Maxime Coquelin <maxime.coquelin@...com>
To:	Arnd Bergmann <arnd@...db.de>,
	Florian Fainelli <f.fainelli@...il.com>
CC:	<tyler.baker@...aro.org>, <linux-kernel@...r.kernel.org>,
	<peter.griffin@...aro.org>, <p.zabel@...gutronix.de>,
	<dinguyen@...nsource.altera.com>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: Allowing reset controllers before SMP initialization (on ARM)?

Hi Florian, Arnd,

On 04/16/2015 10:04 AM, Arnd Bergmann wrote:
> On Wednesday 15 April 2015 17:51:18 Florian Fainelli wrote:
>> Hi,
>>
>> In order to support initialization of the secondary core on BCM63138
>> SoCs, I would want to utilize a reset controller to release the
>> secondary CPU from reset [1].
>>
>> Here are multiple options:
>>
>> - expose a custom function which registers the reset controller platform
>> driver as early as possible, which is probably acceptable, but also
>> requires the DT machine descriptor to populate the platform bus earlier,
>> which we could completely avoid
> I think populating the platform bus earlier is not realistic, that
> would break lots of existing dependencies. In particular, we can't
> do it much earlier because it has to be done after the platform bus
> itself is instantiated.
>
>> - have a OF_DECLARE_RESET_CONTROLLER() which is running fairly early
>> during boot, such that we can utilize reset controllers are early as
>> possible,  before any initcall level, and before SMP initialization is
>> kicking in
> We've added a couple of those, and it could be done here, but putting
> them in the right order is a bit tricky, and I think we can avoid it.

I have already proposed a OF_DECLARE_RESET_CONTROLLER() implementation:
https://lkml.org/lkml/2015/2/20/395

I needed it for the STM32 timers, but it was not accepted.
Now, I perform the timers reset in the bootloader, but it shouldn't work 
in your case.

Kind regards,
Maxime
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