Re: [Xen-devel] Xen on ARM DT based boot protocol

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2013-05-23 at 13:39 +0100, Stefano Stabellini wrote:
> Hi Ian,
> Andre was pointing out to me today that the current boot protocol has a
> problem:
> 
> 
> chosen {
>               bootargs = "dom0_mem=128M console=com1,vga";
>               xen,dom0-bootargs = "earlyprintk=xenboot console=ttyAMA1 
> root=/dev/mmcblk0 debug rw init=/bin/bash";
> };
> 
> 
> because we are using bootargs for Xen arguments, the bootloader cannot
> just pass the same two lines to Xen on ARM and to Linux on ARM.
> It would make their life easier if we had instead:
> 
> 
> chosen {
>               xen,xen-bootarg = "dom0_mem=128M console=com1,vga";
>               bootargs = "earlyprintk=xenboot console=ttyAMA1 
> root=/dev/mmcblk0 debug rw init=/bin/bash";
> };

You mean that instead of 
        if (xen /*or whatever*/) {
                add("bootargs", xencmd);
                add("xen,dom0-bootargs", lcmd);
        } else
                add("xen,xen-bootargs", xencmd);
                add("bootargs", lcmd);
        }
they can have:
        add("bootargs", lcmd);
        if (xen /*or whatever*/) {
                add("xen,xen-bootargs", xencmd);
        }
? Seems like the bootloader needs to know about Xen either way?

Regardless I suppose it's a harmless enough change, although it has
knock on affects on the dom0 dtb creation stuff etc so it might be
useful to see a proposed patch.

What about docs/misc/arm/device-tree/booting.txt though? Or more
generally the fact that the xen,dom0-bootargs "protocol" is really just
a quick hack and not the final thing we actually want bootloaders to
implement (we really want multiboot2 or something).

> Are we still on time to make this change on 4.3?

I think if we think it is definitely the right thing to do we can/should
just do it.

Ian.


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