linux-kernel - Re: [PATCH 2/2] drivers/core/of: Add symlink to device-tree from devices with an OF node

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Date:	Tue, 17 Feb 2015 07:09:19 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Rob Herring <robherring2@...il.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Grant Likely <grant.likely@...aro.org>,
	Olof Johansson <olof@...om.net>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 2/2] drivers/core/of: Add symlink to device-tree from
 devices with an OF node

On Tue, Feb 17, 2015 at 09:00:47AM -0600, Rob Herring wrote:
> +GregKH
> 
> On Sun, Feb 15, 2015 at 9:59 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)
> > properties 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
> > these days.
> >
> > This patch achieves this by adding an "of_node" symlink to devices that
> > have a non-NULL dev->of_node pointer.
> 
> Doesn't this need sysfs documentation?

Yes it does.

> > Signed-off-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> 
> I don't mind applying, but this is Greg's code.
> 
> Rob
> 
> > ---
> >  drivers/base/core.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > index 97e2baf..61ef574 100644
> > --- a/drivers/base/core.c
> > +++ b/drivers/base/core.c
> > @@ -469,6 +469,7 @@ static int device_add_attrs(struct device *dev)
> >  {
> >         struct class *class = dev->class;
> >         const struct device_type *type = dev->type;
> > +       struct device_node *of_node;
> >         int error;
> >
> >         if (class) {
> > @@ -493,6 +494,13 @@ static int device_add_attrs(struct device *dev)
> >                         goto err_remove_dev_groups;
> >         }
> >
> > +       of_node = dev_of_node(dev);
> > +       if (of_node) {
> > +               error = sysfs_create_link(&dev->kobj, &of_node->kobj, "of_node");
> > +               if (error)
> > +                       dev_warn(dev, "Error %d creating of_node link\n", error);
> > +       }

You don't clean up the link when the device is removed?

And why do it here and not in device_add_class_symlinks() like all other
devices do?

thanks,

greg k-h
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