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

[Andre Przywara <andre.przywara@xxxxxxxxxxx>]

On 05/31/2013 04:24 PM, Ian Campbell wrote:
> On Fri, 2013-05-31 at 15:45 +0200, Andre Przywara 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.
> > If you like this approach, I will send the u-boot patch to their ML.
> I think I've traced through all 8 possibilities and the results seem to
> make sense...
Sorry about the coding style issues, I am doing u-boot/Linux/Xen context 
switching currently. Some of the braces are leftovers from debugging (to 
check all 8 possibilities ;-)
Will send a fixed version.

Thanks for the review,
Andre.

> > Signed-off-by: Andre Przywara <andre.przywara@xxxxxxxxxxx>
> > ---
> >   xen/arch/arm/domain_build.c | 14 +++++++++++---
> >   xen/common/device_tree.c    |  7 ++++++-
> >   2 files changed, 17 insertions(+), 4 deletions(-)
> >
> > diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> > index b92c64b..952adb3 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 &&
> > @@ -169,12 +170,19 @@ 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;
> >                   continue;
> > -            else if ( strcmp(prop_name, "xen,dom0-bootargs") == 0 )
> > +            }
> > +            if ( strcmp(prop_name, "bootargs") == 0 )
> >               {
> > -                if ( !bootargs )
> > +                if ( !bootargs  && !had_dom0_bootargs ) {
> >                       bootargs = prop_data;
> > +                }
> Xen coding style doesn't require {} around single lines.
>
> >                   continue;
> >               }
> >           }
> > diff --git a/xen/common/device_tree.c b/xen/common/device_tree.c
> > index 84d704d..c25e6d4 100644
> > --- a/xen/common/device_tree.c
> > +++ b/xen/common/device_tree.c
> > @@ -325,7 +325,12 @@ const char *device_tree_bootargs(const void *fdt)
> >       if ( node < 0 )
> >           return NULL;
> >
> > -    prop = fdt_get_property(fdt, node, "bootargs", NULL);
> > +    prop = fdt_get_property(fdt, node, "xen,xen-bootargs", NULL);
> > +    if ( prop == NULL ) {
> Coding style is { on the next line
>
> > +       if (fdt_get_property(fdt, node, "xen,dom0-bootargs", NULL)) {
> > +            prop = fdt_get_property(fdt, node, "bootargs", NULL);
> > +        }
> There's a hard tab here, but you don't need the {} anyway. To avoid
> ambiguity I would stick with the outer one though.
>
> > +    }
> >       if ( prop == NULL )
> >           return NULL;

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