Re: [Qemu-devel] ARM cpu object, setting properties from board model

[Andreas Färber]

Am 19.11.2013 21:01, schrieb Peter Maydell:
> I find myself with a use case where I would like to set
> a CPU object property from the board model init function
> (specifically, I'd like the board model to be able to say
> "this CPU will boot via PSCI so if you're KVM then start
> it appropriately").
> 
> I could just reach in and fiddle with the ARMCPU field
> the way hw/arm/highback.c does with reset_cbar (and in fact
> that's what I'm likely to do for the moment). However it
> seems like it would be nicer for it to be an official
> QOM property. This is alas not currently possible because
> cpu_arm_init() does both 'init' and 'realize', and once
> you've called it it's too late to set properties.
> 
> Andreas -- did you have any thoughts/plans/code in this area?
> Splitting the realize part out of cpu_arm_init(), or
> providing a cpu_arm_init_dont_realize() [ugh], would be
> easy to code but is it going in the right direction?

My first thought without reviewing the code is to just inline
object_new() followed by object_property_set_bool() in the machine -
that's what I've done for my downstream rl78, where I needed to postpone
realizing the CPU until the firmware blob had been loaded (similar to
armv7m, you may remember pointing me to that example :)).

You are free to split cpu_arm_init() into calling a non-realizing
function, followed by the realization step, then you can reuse that in
multiple places if needed. Mid-term I intend cpu_*_init() to not realize
the CPU - for boards that is waiting on the recursive realization
support, so that only *-user would need to manually realize the CPU.

I would by contrast caution not to blindly use global properties for
cpu_arm_init() since mixed cores are getting more and more common. For
x86 that is much less problematic.

Regards,
Andreas

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