linux-kernel - Re: [RFC/PATCH 2/5] device property: introduce notion of subnodes for legacy boards

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Message-ID: <20180921233336.GB44099@dtor-ws>
Date:   Fri, 21 Sep 2018 16:33:36 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        linux-input@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [RFC/PATCH 2/5] device property: introduce notion of subnodes
 for legacy boards

On Thu, Sep 20, 2018 at 01:16:48PM +0300, Heikki Krogerus wrote:
> On Wed, Sep 19, 2018 at 10:13:26AM -0700, Dmitry Torokhov wrote:
> > > > diff --git a/drivers/base/pset_property.c b/drivers/base/pset_property.c
> > > > index 08ecc13080ae..63f2377aefe8 100644
> > > > --- a/drivers/base/pset_property.c
> > > > +++ b/drivers/base/pset_property.c
> > > > @@ -18,6 +18,11 @@ struct property_set {
> > > >  	struct device *dev;
> > > >  	struct fwnode_handle fwnode;
> > > >  	const struct property_entry *properties;
> > > > +
> > > > +	struct property_set *parent;
> > > > +	/* Entry in parent->children list */
> > > > +	struct list_head child_node;
> > > > +	struct list_head children;
> > > 
> > > Add
> > > 
> > >         const char *name;
> > > 
> > > and you can implement also pset_get_named_child_node().
> > 
> > Or
> > 	char name[];
> > 
> > to avoid separate allocation.
> 
> Let's not do that, especially if you are planning on exporting this
> structure.

Can you please elaborate why? Not using pointer saves us 4/8 bytes +
however much memory we need for bookkeeping for the extra chunk. Given
that majority of pset nodes are unnamed this seems wasteful.

> If the name is coming from .rodata, there is no need to
> allocate anything for the name. Check kstrdup_const().

The data is most likely coming as __initconst so we do need to copy it.

> 
> > Alternatively, we can add it later when we need it, and add
> > device_add_named_child_properties().
> > 
> > I'll leave it up to Rafael to decide.
> 
> Fair enough.
> 
> 
> Thanks,
> 
> -- 
> heikki

Thanks.

-- 
Dmitry