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

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 18 Jun 2019, Julien Grall wrote:
> 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?

Yes, it would be trivial to maintain something like that.

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