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

Hello all.

Sorry for the top-posting.

> I have also CCed Oleksandr, who IIRC worked on a platform using the same SoC
> (DRA7) in the past.

Yes. I worked with DRA7 sometime ago. Unfortunately, I don't remember this platform in details, but, there is a Wiki page describing how to run Xen on this platform which *may* help:
Please note, it is related to old Xen and TI GLSDK versions.

Regarding secondary CPU boot.
The special monitor API is used to enable Hyp mode. U-Boot brings secondary CPU up, which, it turn, switches to Hyp mode and enters WFE until Xen wakes it up.
Take a look at the following patch:


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From: Julien Grall <julien.grall@xxxxxxx>
Sent: Monday, June 17, 2019 13:09
To: Iain Hunter; Denis Obrezkov
Cc: xen-users@xxxxxxxxxxxxxxxxxxxx; Stefano Stabellini; Hunyue Yau; Andre Przywara; Oleksandr Tyshchenko
Subject: Re: Starting to port xen on beagleboard-x15 (GSoC 2019 project)
(+ Andre and Oleksandr)

Hi Denis & lain,

I have discussed with Andre Przywara (in CC) who did some work around
virtualization support in U-boot.

I have also CCed Oleksandr, who IIRC worked on a platform using the same SoC
(DRA7) in the past.

On 17/06/2019 10:03, Iain Hunter wrote:
> I can't remember the history of that patch. What I couldn't figure out
> today was what its effect would be.  I could not find any u-boot code
> that used the CONFIG_XXX values added in the patch.
> So, best ignore it.

lain, did you manage to get SMP working back then?

> Do you have an emulator available yet?
> If so the easiest way I found to debug this type of issue was to:
> 1. Insert an infinite loop just before where I thought I had a problem
>     - in a .S file with
>   loopHere: b loopHere
> - in a C file with
> volatile unsigned char loopHere=1;
> function()
> {  ....
>     while(loopHere);
>     ....
> }
> 2 boot the board
> 3 connect the emulator to the target and then load the symbols for the
> executable (u-boot.img or xen)
> 4 in the emulator set the PC to first instruction after the loop and
> then step over the code. Then you can check the register values to see
> if hypevisor is enabled etc

Both CPUs are Cortex-A15, hence virtualization should be supported. It is a
matter of correctly initializing the secondary CPU.

The platform is not using PSCI but instead a custom SMP bring-up (see
omap5_smp_init in Xen). From my understanding the ROM should bring-up the
secondary CPU to hyp mode if the boot CPU is in hyp mode.

It would be interesting to try Linux on baremetal and see if it brings-up the
secondary CPUs in hyp mode. If it does, then it seems that the problem lies in
Xen. Otherwise it would be in the ROM.

On a side note, I would not spend too much time looking at the SMP now. Instead
you can disable the secondary CPUs.


Julien Grall
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