Re: [Xen-devel] [PATCH v1 4/4] xen/arm: Reuse R-Car Gen2 platform code for Stout board

[Julien Grall <julien.grall@xxxxxxx>]

Hi Oleksandr,

On 08/10/2018 12:47 PM, Oleksandr Tyshchenko wrote:
> On Fri, Aug 10, 2018 at 12:44 PM, Julien Grall <julien.grall@xxxxxxx> wrote:
> > On 08/09/2018 07:18 PM, Oleksandr Tyshchenko wrote:
> > > On Thu, Aug 9, 2018 at 7:20 PM, Julien Grall <julien.grall@xxxxxxx> wrote:
> > > > On 08/09/2018 05:18 PM, Oleksandr Tyshchenko wrote:
> > I am quite confused here. If a CPU will be in hypervisor mode for Xen, how
> > come the same CPU will boot in monitor mode for Linux? Surely there should
> > be no difference in term of boot here. Are you using different firmware
> > here?
> Yes, in order to run modified U-Boot is used. You can see here what
> exactly was modified.
> This instruction [1] contains link to patches [2] (see "Apply
> additional patches" step)
> which should be applied to bare U-Boot.
I don't think it is reasonable to request a specific U-boot just for 
Xen. What if the user decide to run Linux on baremetal? Will he have to 
switch back and forth between firmware?
> [1] 
> https://wiki.xenproject.org/wiki/Xen_ARM_with_Virtualization_Extensions/Lager
> [2] https://lists.xenproject.org/archives/html/xen-devel/2015-01/msg02475.html
>
> > > U-Boot brings non-boot cores up (using ported from Linux's
> > > platsmp-apmu code functions). Then U-Boot switches all cores to HYP
> > > mode.
> >
> > Who did the port? Is it upstream?
> AFAIR Iurii Konovalenko did this port, he is also an author of
> xen/arch/arm/platforms/rcar2.c.
> I don't think U-Boot changes are upsteamed. But anybody who wants to
> run Xen on Lager board is able (I think) to apply
> published patches [2] to U-Boot and build it.
> The same way anybody who will want to run Xen on Stout board will be able
> to apply U-Boot patches I will attach to the future Wiki page for Stout board.
I am a bit concerned that patch for lager has never been upstreamed. Is 
it at least part of the Renesas BSP?
What's the plan for Stout support?

> > > While jump into Xen on a boot core, all non-boot cores are left in
> > > U-Boot to wait to be "woken up by Xen" (actually rcar2_smp_init() is
> > > used for).
> > > Platform R-Car2 code in Xen doesn't power on cores, it just "brings
> > > them to Xen".
> >
> > What does the address 0xe63c0000 corresponds too? From the DT it seems it is
> > part of the ICRAM. But it is not clear why you write in there.
> Yes, it is a part of the ICRAM.
>
> Unfortunately, I am not an expert in such code to definitively say how
> it is supposed to work.
> But it seems that 0xE63C0FFC is an address which is being polled by
> non-boot core in U-Boot. It was set to zero value
> beforehand. So, writing an actual value to this address, Xen triggers
> an action for bringing non-boot core up to Xen.
>
> Waiting loop in U-Boot:
>
> asm(".arm \n"
> ".align 2 \n"
> ".global smp_waitloop \n"
> "smp_waitloop: \n"
> "1: wfe \n"
> "ldr r0, =0xE63C0FFC \n"
> "ldr r0, [r0] \n"
> "teq r0, #0x0 \n"
> "beq 1b \n"
>    "b _do_nonsec_entry \n"
> ".type smp_waitloop, %function \n"
> ".size smp_waitloop, .-smp_waitloop \n");
>
> Trigger code in Xen:
>
> writel(__pa(init_secondary), 0xE63C0FFC);
>
> > Could you point to any relevant documentation?
> I am afraid, I can't point to documentation.
While the code was added for Lager and you just piggy-back on it,
if you already hack U-boot to bring-up CPUs in hyp mode, then you better 
add PSCI support.
To be honest, the lager support was likely accepted based on the code 
would make the way to Upstream. It is now been 3 years without any 
change. If there are no plan to address that, then I will send a patch 
to drop the support for Lager in Xen.
Cheers,

--
Julien Gral

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