Standard/common method for booting secondary cores

[slash.tmp@free.fr (Mason)]

Hello Dave,

It seems you and Mark posted within seconds of each other :-)

On 21/04/2015 13:41, Dave Martin wrote:
> On Tue, Apr 21, 2015 at 12:43:03AM +0200, Mason wrote:
>> Hello,
>>
>> With the current push for CONFIG_ARCH_MULTIPLATFORM,
>> I'm wondering if things like starting secondary cores
>> have been "standardized"/factorized to the point where
>> I can just use some default implementation?
>>
>> I think the implementation I'm using as a starting
>> point uses SMC calls. I think we are using "TrustZone"
>> where Linux runs in NS (non secure) mode, and a tiny
>> proprietary OS runs in secure mode.
>
> _If_ you're implementing something new

You're talking about software, right?
(The hardware already exists.)
As I mentioned we do have a working implementation using
SMC to request service from the secure OS, but I have some
time to evaluate "better" strategies, as I port the
platform to a newer kernel.

> and have a say in what gets implemented in the firmware,
> please consider PSCI.

In this context, firmware would be the code run by the
secure OS?

> Without this, little standardisation exists.  Low level CPU
> power management must typically involve SMCs, but there's
> no standardisation of their exact semantics, which implies that
> some platform-specific glue will likely be needed.  The best you can
> do is look for one or more backends in the kernel that are
> close to what you need (if any), and if so propose some refactoring
> to extend support to your platform.

My objective is to minimize platform-specific code, I will
look into PSCI.

>> IIUC (which is probably NOT the case), when Linux runs
>> in NS mode, some operations that are typically carried
>> out at boot/init are not allowed, such as
>>
>> - starting secondary cores
>> - configuring the L2 cache controller
>>
>> and this must be done by the secure OS via SMC?
>
> Generally, yes.

Is PSCI involved in L2$ configuration?

>> I'd be happy to be given pointers to internet references
>> and do my own reading. I've bookmarked a few on related
>> subjects:
>>
>> http://events.linuxfoundation.org/sites/events/files/slides/clement-smp-bring-up-on-arm-soc.pdf
>> http://www.linux-arm.org/pub/LinuxPlatform/RealViewLink/Booting_ARM_Linux_SMP_on_MPCore.doc
>> http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0388g/Beihjjgb.html
>> http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.prd29-genc-009492c/index.html
>
> For PSCI, you can look at http://infocenter.arm.com/help/topic/com.arm.doc.den0022c/index.html.
>
>>
>> Are the arch/arm/common/mcpm_* files relevant?
>
> MCPM is infrastructure for handling _cluster_ powerup/powerdown, in
> kernels where Linux runs in Secure (or otherwise has a high level of
> access to power controls).
>
> If unsure, say N.

Thanks.