Re: [XenARM] Question about booting parameter of Mini-OS for ARM

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2013-05-06 at 11:40 +0100, Stefano Stabellini wrote:
> On Mon, 6 May 2013, Chen Baozi wrote:
> > On Mar 25, 2013, at 6:00 PM, Stefano Stabellini 
> > <Stefano.Stabellini@xxxxxxxxxxxxx> wrote:
> > 
> > > On Sun, 24 Mar 2013, Chen Baozi wrote:
> > >> Hi all,
> > >> 
> > >> I'm reading Mini-OS's codes and to estimate the amount of work porting 
> > >> it to
> > >> ARM (Ian's GSoC idea this year).
> > >> 
> > >> While Xen is booting Mini-OS on x86 platform, it passes the start_info_t 
> > >> to
> > >> the guest through ESI register. And Mini-OS would use this structure as 
> > >> the 
> > >> argument of start_kernel. However, I didn't see codes handle the
> > >> start_info_t on ARM side. Instead, I see a more standard protocal when
> > >> booting ARM's dom0, which follows linux kernel bootstrap rules:
> > >> 
> > >>  r0 = 0, r1 = machine nr, r2 = atags or dtb pointer
> > >> 
> > >> Does it mean that Xen for ARM does not use the start_info_t to pass
> > >> information when booting PV guest? 
> > >> Or did I miss something important?
> > > 
> > > That's right, we don't use start_info_t on ARM, in fact ARM guests are
> > > not exactly like x86 PV guests.
> > > The information present in the start_info page are either available via
> > > device tree or no used on ARM.
> > 
> > I'm thinking of parsing the dtb and fill the start_info structure
> according to it before jump to the start_kernel. In that case, it
> won't break some original mini-os interface.

If you go this path then trying to do it in arch_init would be
preferable. Nothing in start_kernel before arch_init seems like it
should need start info.

This is effectively what we do for Linux guests too -- populate a stunt
start info early on.

> You can try that, or you can refactor the code dividing it into x86
> specific and common stuff.

There is bound to be a bunch of this sort of refactoring required, just
because mini-os in practice has only really supported x86 until now and
even with the best intentions arch specific stuff tends to leak out
unless you are actively using something on multiple arches.

Ian.



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