Re: [Xen-devel] Starting to port xen on beagleboard-x15 (GSoC 2019 project)

[Julien Grall <julien.grall@xxxxxxx>]

On 18/06/2019 13:28, Andrii Anisov wrote:
> +xen-devel
Please don't cross-post e-mail. If you move the thread to xen-devel, then 
xen-users should be droppped.
> Hello Julien,
>
> > I am a bit confused. Linux is able to bring-up CPU in hyp mode with the current
> > U-boot. Why would we need more changes for Xen?
> TI's ROM code starts all CPUs in NS PL1, doesn't matter if it is boot or 
> secondary core.
> If you look at Linux code [1], you'll see, that after the secondary core 
> bringup Linux does switch that core from NS PL1 to PL2 (hyp mode) using ROM 
> code interface (smc 0).
> At some moment XEN dropped all to-hyp-mode switching code. So I did switch 
> secondaries to hyp mode in u-boot with the loop which replicates the ROM Code 
> logic in terms of waiting for an event and checking aux registers.
Switch to hyp-mode is fairly complex and depends on your processor. Hence why it 
was dropped in both Linux and Xen.
However, calling an SMC would be acceptable to me. Stefano, any opinion?

> [1] 
> https://elixir.bootlin.com/linux/v5.1/source/arch/arm/mach-omap2/omap-headsmp.S#L62
[...]

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Cheers,

--
Julien Grall

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