linux-kernel - Re: [PATCH 1/2] drivers: base: swnode: link devices to software nodes

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Date:   Mon, 29 Jul 2019 15:15:32 +0200
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>,
        "Enrico Weigelt, metux IT consult" <info@...ux.net>,
        linux-input@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Andy Shevchenko <andy.shevchenko@...il.com>
Subject: Re: [PATCH 1/2] drivers: base: swnode: link devices to software nodes

On Mon, Jul 29, 2019 at 03:07:15PM +0300, Heikki Krogerus wrote:
> On Sat, Jul 13, 2019 at 12:52:58AM -0700, Dmitry Torokhov wrote:
> > It is helpful to know what device, if any, a software node is tied to, so
> > let's store a pointer to the device in software node structure. Note that
> > children software nodes will inherit their parent's device pointer, so we
> > do not have to traverse hierarchy to see what device the [sub]tree belongs
> > to.
> > 
> > We will be using the device pointer to locate GPIO lookup tables for
> > devices with static properties.
> > 
> > Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
> > ---
> >  drivers/base/property.c  |  1 +
> >  drivers/base/swnode.c    | 35 ++++++++++++++++++++++++++++++++++-
> >  include/linux/property.h |  5 +++++
> >  3 files changed, 40 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/base/property.c b/drivers/base/property.c
> > index 348b37e64944..3bc93d4b35c4 100644
> > --- a/drivers/base/property.c
> > +++ b/drivers/base/property.c
> > @@ -527,6 +527,7 @@ int device_add_properties(struct device *dev,
> >  	if (IS_ERR(fwnode))
> >  		return PTR_ERR(fwnode);
> >  
> > +	software_node_link_device(fwnode, dev);
> >  	set_secondary_fwnode(dev, fwnode);
> >  	return 0;
> >  }
> > diff --git a/drivers/base/swnode.c b/drivers/base/swnode.c
> > index 7fc5a18e02ad..fd12eea539b6 100644
> > --- a/drivers/base/swnode.c
> > +++ b/drivers/base/swnode.c
> > @@ -24,6 +24,9 @@ struct software_node {
> >  
> >  	/* properties */
> >  	const struct property_entry *properties;
> > +
> > +	/* device this node is associated with */
> > +	struct device *dev;
> >  };
> 
> Let's not do that! The nodes can be, and in many cases are, associated
> with multiple devices.

They do? Where? I see that set of properties can be shared between
several devices, but when we instantiate SW node we create a new
instance for device. This is also how ACPI and OF properties work; they
not shared between devices (or, rather, the kernel creates distinct _and
single_ devices for instance of ACPI or OF node). I do not think we want
swnodes work differently from the other firmware nodes.

> 
> Every device is already linked with the software node kobject, so
> isn't it possible to simply walk trough those links in order to check
> the devices associated with the node?

No, we need to know the exact instance of a device, not a set of
devices, because even though some properties can be shared, others can
not. For example, even if 2 exactly same touch controllers in the system
have "reset-gpios" property, they won't be the same GPIO for the both of
them.

Thanks.

-- 
Dmitry