Subject: Re: [PATCH 3/5] of/device: Make of_get_next_child() check status properties

From: David Gibson <[email-masked]>
Date: Thu, 9 Dec 2010 14:09:24 +1100

On Thu, Dec 09, 2010 at 12:33:22PM +1100, Michael Ellerman wrote:
> On Wed, 2010-12-08 at 15:01 -0600, Scott Wood wrote:
> > On Wed, 8 Dec 2010 11:29:44 -0800
> > Deepak Saxena <[email-masked]> wrote:
> > 
> > > We only return the next child if the device is available.
> > > 
> > > Signed-off-by: Hollis Blanchard <[email-masked]>
> > > Signed-off-by: Deepak Saxena <[email-masked]>
> > > ---
> > >  drivers/of/base.c |    4 +++-
> > >  1 files changed, 3 insertions(+), 1 deletions(-)
> > > 
> > > diff --git a/drivers/of/base.c b/drivers/of/base.c
> > > index 5d269a4..81b2601 100644
> > > --- a/drivers/of/base.c
> > > +++ b/drivers/of/base.c
> > > @@ -321,6 +321,8 @@ struct device_node *of_get_next_parent(struct device_node *node)
> > >   *
> > >   *	Returns a node pointer with refcount incremented, use
> > >   *	of_node_put() on it when done.
> > > + *
> > > + *	Does not return nodes marked unavailable by a status property.
> > >   */
> > >  struct device_node *of_get_next_child(const struct device_node *node,
> > >  	struct device_node *prev)
> > > @@ -330,7 +332,7 @@ struct device_node *of_get_next_child(const struct device_node *node,
> > >  	read_lock(&devtree_lock);
> > >  	next = prev ? prev->sibling : node->child;
> > >  	for (; next; next = next->sibling)
> > > -		if (of_node_get(next))
> > > +		if (of_device_is_available(next) && of_node_get(next))
> > >  			break;
> > >  	of_node_put(prev);
> > >  	read_unlock(&devtree_lock);
> > 
> > This seems like too low-level a place to put this.  Some code may know
> > how to un-disable a device in certain situations, or it may be part of
> > debug code trying to dump the whole device tree, etc.  Looking
> > further[1], I see a raw version of this function, but not other things
> > like of_find_compatible_node.
> 
> Yeah I agree. I think we'll eventually end up with __ versions of all or
> lots of them. Not to mention there might be cases you've missed where
> code expects to see unavailable nodes. The right approach is to add
> _new_ routines that don't return unavailable nodes, and convert code
> that you know wants to use them.

Actually, I don't think we really want these status-skipping
iterators at all.  The device tree iterators should give us the device
tree, as it is.  Those old-style drivers which seach for a node rather
than using the bus probing logic can keep individual checks of the
status property until they're converted to the new scheme.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson