linux-kernel - Re: [PATCH v2 1/6] software node: Provide replacement for device_add

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Message-ID: <CAJZ5v0j+fTG4rw6Z9XU9h=UFSObT5s2a=EY21g5YYyk9BDNtsQ@mail.gmail.com>
Date:   Thu, 4 Feb 2021 17:06:53 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Felipe Balbi <balbi@...nel.org>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:ULTRA-WIDEBAND (UWB) SUBSYSTEM:" 
        <linux-usb@...r.kernel.org>
Subject: Re: [PATCH v2 1/6] software node: Provide replacement for device_add_properties()

On Thu, Feb 4, 2021 at 3:17 PM Heikki Krogerus
<heikki.krogerus@...ux.intel.com> wrote:
>
> At the moment the function device_del() is calling
> device_remove_properties() unconditionally. That will result into the
> reference count of the software node attached to the device being
> decremented, and in most cases it will hit 0 at that point. So in
> practice device_del() will unregister the software node attached to
> the device, even if that was not the intention of the caller. Right
> now software nodes can not be reused or shared because of that.
>
> So device_del() can not unregister the software nodes unconditionally
> like that. Unfortunately some of the users of device_add_properties()
> are now relying on this behaviour. Because of that, and also in
> general, we do need a function that can offer similar behaviour where
> the lifetime of the software node is bound to the lifetime of the
> device. But it just has to be a separate function so the behaviour is
> optional. We can not remove the device_remove_properties() call from
> device_del() before we have that new function, and before we have
> replaced device_add_properties() calls with it in all the places that
> require that behaviour.
>
> This adds function device_create_managed_software_node() that can be
> used for exactly that purpose. Software nodes created with it are
> declared "managed", and separate handling for those nodes is added to
> the software node code. The reference count of the "managed" nodes is
> decremented when the device they are attached to is removed. This will
> not affect the other nodes that are not declared "managed".
>
> The function device_create_managed_software_node() has also one
> additional feature that device_add_properties() does not have. It
> allows the software nodes created with it to be part of a node
> hierarchy by taking also an optional parent node as parameter.
>
> Signed-off-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>

The rationale is clear now, so

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

and I'm assuming that this will be routed via the USB tree.

> ---
>  drivers/base/swnode.c    | 43 ++++++++++++++++++++++++++++++++++++++++
>  include/linux/property.h |  4 ++++
>  2 files changed, 47 insertions(+)
>
> diff --git a/drivers/base/swnode.c b/drivers/base/swnode.c
> index 20faa9f4f5ed2..37179a8b1ceba 100644
> --- a/drivers/base/swnode.c
> +++ b/drivers/base/swnode.c
> @@ -24,6 +24,7 @@ struct swnode {
>         struct swnode *parent;
>
>         unsigned int allocated:1;
> +       unsigned int managed:1;
>  };
>
>  static DEFINE_IDA(swnode_root_ids);
> @@ -1045,6 +1046,43 @@ void device_remove_software_node(struct device *dev)
>  }
>  EXPORT_SYMBOL_GPL(device_remove_software_node);
>
> +/**
> + * device_create_managed_software_node - Create a software node for a device
> + * @dev: The device the software node is assigned to.
> + * @properties: Device properties for the software node.
> + * @parent: Parent of the software node.
> + *
> + * Creates a software node as a managed resource for @dev, which means the
> + * lifetime of the newly created software node is tied to the lifetime of @dev.
> + * Software nodes created with this function should not be reused or shared
> + * because of that. The function takes a deep copy of @properties for the
> + * software node.
> + *
> + * Since the new software node is assigned directly to @dev, and since it should
> + * not be shared, it is not returned to the caller. The function returns 0 on
> + * success, and errno in case of an error.
> + */
> +int device_create_managed_software_node(struct device *dev,
> +                                       const struct property_entry *properties,
> +                                       const struct software_node *parent)
> +{
> +       struct fwnode_handle *p = software_node_fwnode(parent);
> +       struct fwnode_handle *fwnode;
> +
> +       if (parent && !p)
> +               return -EINVAL;
> +
> +       fwnode = fwnode_create_software_node(properties, p);
> +       if (IS_ERR(fwnode))
> +               return PTR_ERR(fwnode);
> +
> +       to_swnode(fwnode)->managed = true;
> +       set_secondary_fwnode(dev, fwnode);
> +
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(device_create_managed_software_node);
> +
>  int software_node_notify(struct device *dev, unsigned long action)
>  {
>         struct swnode *swnode;
> @@ -1073,6 +1111,11 @@ int software_node_notify(struct device *dev, unsigned long action)
>                 sysfs_remove_link(&swnode->kobj, dev_name(dev));
>                 sysfs_remove_link(&dev->kobj, "software_node");
>                 kobject_put(&swnode->kobj);
> +
> +               if (swnode->managed) {
> +                       set_secondary_fwnode(dev, NULL);
> +                       kobject_put(&swnode->kobj);
> +               }
>                 break;
>         default:
>                 break;
> diff --git a/include/linux/property.h b/include/linux/property.h
> index b0e413dc59271..dafccfce02624 100644
> --- a/include/linux/property.h
> +++ b/include/linux/property.h
> @@ -491,4 +491,8 @@ void fwnode_remove_software_node(struct fwnode_handle *fwnode);
>  int device_add_software_node(struct device *dev, const struct software_node *swnode);
>  void device_remove_software_node(struct device *dev);
>
> +int device_create_managed_software_node(struct device *dev,
> +                                       const struct property_entry *properties,
> +                                       const struct software_node *parent);
> +
>  #endif /* _LINUX_PROPERTY_H_ */
> --
> 2.30.0
>