linux-kernel - Re: [PATCH] drivers/core/of: Add symlink to device-tree from devices with an OF node

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Date:	Wed, 19 Nov 2014 13:30:27 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Rob Herring <robherring2@...il.com>
Cc:	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>,
	Grant Likely <grant.likely@...aro.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	Jeremy Kerr <jeremy.kerr@....ibm.com>
Subject: Re: [PATCH] drivers/core/of: Add symlink to device-tree from
 devices with an OF node

On Tue, 2014-11-18 at 10:37 -0600, Rob Herring wrote:
> On Wed, Nov 12, 2014 at 7:10 PM, Benjamin Herrenschmidt
> <benh@...nel.crashing.org> wrote:
> > So I've been annoyed lately with having a bunch of devices such as i2c
> > eeproms (for use by VPDs, server world !) and other bits and pieces that
> > I want to be able to identify from userspace, and possibly provide
> > additional data about from FW.
> >
> > Basically, it boils down to correlating the sysfs device with the OF
> > tree device node, so that user space can use device-tree info such as
> > additional "location" or "label" (or whatever else we can come up with)
> > propreties to identify a given device, or get some attributes of use
> > about it, etc...
> >
> > Now, so far, we've done that in some subsystem in a fairly ad-hoc basis
> > using "devspec" properties. For example, PCI creates them if it can
> > correlate the probed device with a DT node. Some powerpc specific busses
> > do that too.
> >
> > However, i2c doesn't and it would be nice to have something more generic
> > since technically any device can have a corresponding device tree node.
> >
> > This patch adds an "of_node" symlink to devices that have a non-NULL
> > dev->of_node pointer, the patch is pretty trivial and seems to work just
> > fine for me.
> >
> > Signed-off-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> > ---
> > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > index 20da3ad..8c7b607 100644
> > --- a/drivers/base/core.c
> > +++ b/drivers/base/core.c
> > @@ -493,6 +493,15 @@ static int device_add_attrs(struct device *dev)
> >                         goto err_remove_dev_groups;
> >         }
> >
> > +#ifdef CONFIG_OF
> > +       if (dev->of_node) {
> 
> if (IS_ENABLED(CONFIG_OF) && dev->of_node)

Ok, I didn't realize the of_node field existed in struct device even
without CONFIG_OF (otherwise that wouldn't have compiled). Grant, Rob,
do you want to take this patch (with the above fixed) or should I not
bother based on the fact that the info is in uevent ? I prefer still
doing the symlink but you tell me.

> > +               error = sysfs_create_link(&dev->kobj, &dev->of_node->kobj,
> > +                                         "of_node");
> > +               if (error)
> > +                       dev_warn(dev, "Error %d creating of_node link\n", error);
> > +       }
> > +#endif /* CONFIG_OF */
> > +
> >         return 0;
> >
> >   err_remove_dev_groups:
> >
> >
> --
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