Re: [Xen-devel] [PATCH V1 08/29] xen/dts: Don't add a fake property "name" in the device tree

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2013-09-09 at 10:30 +0100, Julien Grall wrote:
> On 09/06/2013 05:28 PM, Ian Campbell wrote:
> > On Wed, 2013-08-28 at 15:47 +0100, Julien Grall wrote:
> >> On new Flat Device Tree version, the property "name" may not exist.
> >> The property is never used in Xen code except to set the field "name" of
> >> dt_device_node.
> >>
> >> For convenience, remove the fake property. It will save space during the
> >> creation of the dom0 FDT.
> >
> > Is it worth diverging from the Linux code this is based on over this
> > though?
> 
> If we don't diverge, I need to add some logic in device tree creation to 
> know if the "name" property was generated by Xen.

Because otherwise it gets included in the DTB given to dom0? Is that
harmful though?

> 
> The others solutions was:
>     1) Add the logic during device tree creation
>     2) Add a boolean to know if the property is a fake

Would it be possible to reduce the divergence, at the cost of a little
bit of dead code by not actually removing the code which makes up the
name, but rather short circuiting it with a "continue" or an "if (0
&&  ...)" (plus an appropriate comment).

> Currently, the "name" property value is replicated in the name field of 
> dt_device_node. Except staying close to Linux code, I don't see a good 
> reason to create this fake property.
> 
> >>
> >> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> >> ---
> >>   xen/common/device_tree.c |   21 +++++++++------------
> >>   1 file changed, 9 insertions(+), 12 deletions(-)
> >>
> >> diff --git a/xen/common/device_tree.c b/xen/common/device_tree.c
> >> index be592d2..07a19ac 100644
> >> --- a/xen/common/device_tree.c
> >> +++ b/xen/common/device_tree.c
> >> @@ -1543,6 +1543,7 @@ static unsigned long __init unflatten_dt_node(const 
> >> void *fdt,
> >>       if ( !has_name )
> >>       {
> >>           char *p1 = pathp, *ps = pathp, *pa = NULL;
> >> +        char *tmp = NULL;
> >>           int sz;
> >>
> >>           while ( *p1 )
> >> @@ -1556,25 +1557,21 @@ static unsigned long __init 
> >> unflatten_dt_node(const void *fdt,
> >>           if ( pa < ps )
> >>               pa = p1;
> >>           sz = (pa - ps) + 1;
> >> -        pp = unflatten_dt_alloc(&mem, sizeof(struct dt_property) + sz,
> >> -                                __alignof__(struct dt_property));
> >> +
> >> +        tmp = unflatten_dt_alloc(&mem, sz, 1);
> >>           if ( allnextpp )
> >>           {
> >> -            pp->name = "name";
> >> -            pp->length = sz;
> >> -            pp->value = pp + 1;
> >> -            *prev_pp = pp;
> >> -            prev_pp = &pp->next;
> >> -            memcpy(pp->value, ps, sz - 1);
> >> -            ((char *)pp->value)[sz - 1] = 0;
> >> -            dt_dprintk("fixed up name for %s -> %s\n", pathp,
> >> -                       (char *)pp->value);
> >> +            memcpy(tmp, ps, sz - 1);
> >> +            np->name = tmp;
> >> +            tmp[sz - 1] = 0;
> >> +            dt_dprintk("fixed up name for %s -> %s\n", pathp, np->name);
> >>           }
> >>       }
> >> +
> >>       if ( allnextpp )
> >>       {
> >>           *prev_pp = NULL;
> >> -        np->name = dt_get_property(np, "name", NULL);
> >> +        np->name = (np->name) ? : dt_get_property(np, "name", NULL);
> >>           np->type = dt_get_property(np, "device_type", NULL);
> >>
> >>           if ( !np->name )
> >
> >
> 
> 



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