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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2013-08-20 at 14:32 +0100, Julien Grall wrote:
> 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 :).

Do the wiki pages use the /modules stuff at all? If not then would not
expect they would use /module/N/bootargs either.

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

I think this is a must. In fact IIRC this was the main reason the patch
wasn't just applied.

Ian.


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