linux-kernel - Re: [PATCH v2 1/6] device property: Add functions for accessing node's parents

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Message-ID: <20190327142036.jf6puc5uo2mjutbl@paasikivi.fi.intel.com>
Date:   Wed, 27 Mar 2019 16:20:37 +0200
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     linux-kernel@...r.kernel.org, rafael@...nel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-acpi@...r.kernel.org, devicetree@...r.kernel.org,
        Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v2 1/6] device property: Add functions for accessing
 node's parents

Hi Petr,

On Wed, Mar 27, 2019 at 01:26:25PM +0100, Petr Mladek wrote:
> On Tue 2019-03-26 14:41:01, Sakari Ailus wrote:
> > Add two convenience functions for accessing node's parents:
> > 
> > fwnode_count_parents() returns the number of parent nodes a given node
> > has. fwnode_get_nth_parent() returns node's parent at a given distance
> > from the node itself.
> > 
> > Also reorder fwnode_get_parent() in property.c according to the same order
> > as in property.h.
> > 
> > diff --git a/drivers/base/property.c b/drivers/base/property.c
> > index 8b91ab380d14..61eb6ceacc3f 100644
> > --- a/drivers/base/property.c
> > +++ b/drivers/base/property.c
> > @@ -554,17 +567,49 @@ struct fwnode_handle *fwnode_get_next_parent(struct fwnode_handle *fwnode)
> >  EXPORT_SYMBOL_GPL(fwnode_get_next_parent);
> >  
> >  /**
> > - * fwnode_get_parent - Return parent firwmare node
> > - * @fwnode: Firmware whose parent is retrieved
> > + * fwnode_count_parents - Return the number of parents a node has
> > + * @fwnode: The node the parents of which are to be counted
> >   *
> > - * Return parent firmware node of the given node if possible or %NULL if no
> > - * parent was available.
> > + * Returns the number of parents a node has.
> >   */
> > -struct fwnode_handle *fwnode_get_parent(const struct fwnode_handle *fwnode)
> > +unsigned int fwnode_count_parents(struct fwnode_handle *fwnode)
> >  {
> > -	return fwnode_call_ptr_op(fwnode, get_parent);
> > +	unsigned int count;
> > +
> > +	fwnode_handle_get(fwnode);
> > +
> > +	for (count = 0; fwnode; count++)
> > +		fwnode = fwnode_get_next_parent(fwnode);
> 
> Is it guaranteed that all parents stay when
> fwnode_get_next_parent() releases the reference count
> for each counted member?

fwnode_get_next_parent() only releases the child node after it has acquired
the parent. The only implementation with refcounting for single nodes is
actually OF.

> 
> > +
> > +	return count - 1;
> 
> We could start counting from count = -1;

We could, but then count would need to be made signed (unless overflowing
is preferred instead).

-- 
Regards,

Sakari Ailus
sakari.ailus@...ux.intel.com