Re: [Xen-devel] [PATCH v2] ARM: parse separate DT properties for different commandlines

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 20 August 2013 14:11, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> On Tue, 2013-08-20 at 13:19 +0100, Julien Grall wrote:
>> On 20 August 2013 13:09, Andre Przywara <andre.przywara@xxxxxxxxxx> wrote:
>> > On 07/10/2013 01:48 PM, Julien Grall wrote:
>> >>
>> >> On 3 June 2013 14:43, Andre Przywara <andre.przywara@xxxxxxxxxxx> wrote:
>> >>>
>> >>> Currently we use the chosen/bootargs property as the Xen commandline
>> >>> and rely on xen,dom0-bootargs for Dom0. However this brings issues
>> >>> with bootloaders, which usually build bootargs by bootscripts for a
>> >>> Linux kernel - and not for the entirely different Xen hypervisor.
>> >>> Introduce a new possible device tree property "xen,xen-bootargs"
>> >>> explicitly for the Xen hypervisor and make the selection of which to
>> >>> use more fine grained:
>> >>> - If xen,xen-bootargs is present, it will be used for Xen.
>> >>> - If xen,dom0-bootargs is present, it will be used for Dom0.
>> >>> - If xen,xen-bootargs is _not_ present, but xen,dom0-bootargs is,
>> >>>    bootargs will be used for Xen. Like the current situation.
>> >>> - If no Xen specific properties are present, bootargs is for Dom0.
>> >>> - If xen,xen-bootargs is present, but xen,dom0-bootargs is missing,
>> >>>    bootargs will be used for Dom0.
>> >>>
>> >>> The aim is to allow common bootscripts to boot both Xen and native
>> >>> Linux with the same device tree blob. If needed, one could hard-code
>> >>> the Xen commandline into the DTB, leaving bootargs for Dom0 to be set
>> >>> by the (non Xen-aware) bootloader.
>> >>> I also have a simple patch for u-boot to transfer the content of the
>> >>> "xen_bootargs" environment variable into the xen,xen-bootargs dtb
>> >>> property.
>> >>> I will post the u-boot patch to their ML later.
>> >>>
>> >>> Changes from v1:
>> >>> - fix whitespace issues
>> >>
>> >>
>> >> Any news about this patch ? :)
>> >
>> >
>> > Sorry for the lag ;-)
>> >
>> >
>> >>
>> >>> Signed-off-by: Andre Przywara <andre.przywara@xxxxxxxxxxx>
>> >>> ---
>> >>>   xen/arch/arm/domain_build.c | 13 ++++++++++---
>> >>>   xen/common/device_tree.c    |  7 ++++++-
>> >>>   2 files changed, 16 insertions(+), 4 deletions(-)
>> >>>
>> >>> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
>> >>> index b92c64b..5809489 100644
>> >>> --- a/xen/arch/arm/domain_build.c
>> >>> +++ b/xen/arch/arm/domain_build.c
>> >>> @@ -139,6 +139,7 @@ static int write_properties(struct domain *d, struct
>> >>> kernel_info *kinfo,
>> >>>                               u32 address_cells, u32 size_cells)
>> >>>   {
>> >>>       const char *bootargs = NULL;
>> >>> +    int had_dom0_bootargs = 0;
>> >>>       int prop;
>> >>>
>> >>>       if ( early_info.modules.nr_mods >= 1 &&
>> >>> @@ -169,11 +170,17 @@ static int write_properties(struct domain *d,
>> >>> struct kernel_info *kinfo,
>> >>>            */
>> >>>           if ( device_tree_node_matches(fdt, node, "chosen") )
>> >>>           {
>> >>> -            if ( strcmp(prop_name, "bootargs") == 0 )
>> >>> +            if ( strcmp(prop_name, "xen,xen-bootargs") == 0 )
>> >>> +                continue;
>> >>> +            if ( strcmp(prop_name, "xen,dom0-bootargs") == 0 )
>> >>> +            {
>> >>> +                had_dom0_bootargs = 1;
>> >>> +                bootargs = prop_data;
>> >>
>> >>
>> >> Here, you overwrite the previous "bootargs". This variable is set if
>> >> the module node contains "bootargs" property
>> >> (see process_multiboot_node in common/device_tree.c)
>> >
>> >
>> > I'd say that is intended. I think those command lines directly under 
>> > /chosen
>> > should have the highest priority. If someone has
>> > /chosen/xen,dom0-bootargs, that should be used instead of a most likely
>> > hard-coded value under modules.
>>
>> I don't  think people use bootargs in module.
>
> They are documented as existing in
> docs/misc/arm/device-tree/booting.txt, so something would need to change
> in either the code or the docs I think.

The wiki page only mentions xen,dom0-bootargs solution :).

BTW, Andre, can you document this patch at least in docs/misc/arm?

> I don't think I mind which options take precedence so long as it is
> clearly documented what is what. Although there is something nice about
> having the stuff under modules be a complete consistent set of address
> +cmdline I guess.

If we plan to use multiboot in the next few months, it's not a good
idea to keep 2 ways
(in fact even 3 now) to set Linux command line.

I guess people mostly follow the wiki page, so they don't you the
module@0/bootargs
solution.

-- 
Julien Grall

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