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SubjectRe: [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@gmail.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

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