linux-kernel - Re: [PATCH V7 1/3] of: dynamic: Add interfaces for creating device node dynamically

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Message-ID: <CAL_Jsq+FM9P0n7BQZBY1AGJRtjAWw9F6h5DYmLkdPeXZaiYJwA@mail.gmail.com>
Date:   Thu, 23 Mar 2023 17:40:39 -0500
From:   Rob Herring <robh@...nel.org>
To:     Lizhi Hou <lizhi.hou@....com>
Cc:     linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, frowand.list@...il.com,
        helgaas@...nel.org, clement.leger@...tlin.com, max.zhen@....com,
        sonal.santan@....com, larry.liu@....com, brian.xu@....com,
        stefano.stabellini@...inx.com, trix@...hat.com
Subject: Re: [PATCH V7 1/3] of: dynamic: Add interfaces for creating device
 node dynamically

On Thu, Jan 19, 2023 at 9:02 PM Lizhi Hou <lizhi.hou@....com> wrote:
>
> of_create_node() creates device node dynamically. The parent device node
> and full name are required for creating the node. It optionally creates
> an OF changeset and attaches the newly created node to the changeset. The
> device node pointer and the changeset pointer can be used to add
> properties to the device node and apply the node to the base tree.
>
> of_destroy_node() frees the device node created by of_create_node(). If
> an OF changeset was also created for this node, it will destroy the
> changeset before freeing the device node.
>
> Expand of_changeset APIs to handle specific types of properties.
>     of_changeset_add_prop_string()
>     of_changeset_add_prop_string_array()
>     of_changeset_add_prop_u32_array()
>
> Signed-off-by: Lizhi Hou <lizhi.hou@....com>

Your Sob should be last because you sent this patch. The order of Sob
is roughly the order of possession of the patch.

> Signed-off-by: Sonal Santan <sonal.santan@....com>
> Signed-off-by: Max Zhen <max.zhen@....com>

So Sonal and Max modified this patch?

> Reviewed-by: Brian Xu <brian.xu@....com>
> Signed-off-by: Clément Léger <clement.leger@...tlin.com>

Why does this have Clément's Sob?

> ---
>  drivers/of/dynamic.c | 197 +++++++++++++++++++++++++++++++++++++++++++
>  include/linux/of.h   |  24 ++++++
>  2 files changed, 221 insertions(+)
>
> diff --git a/drivers/of/dynamic.c b/drivers/of/dynamic.c
> index cd3821a6444f..4e211a1d039f 100644
> --- a/drivers/of/dynamic.c
> +++ b/drivers/of/dynamic.c
> @@ -461,6 +461,71 @@ struct device_node *__of_node_dup(const struct device_node *np,
>         return NULL;
>  }
>
> +/**
> + * of_create_node - Dynamically create a device node

For consistency, I think this should be of_changeset_create_node().

> + *
> + * @parent: Pointer to parent device node
> + * @full_name: Node full name
> + * @cset: Pointer to returning changeset
> + *
> + * Return: Pointer to the created device node or NULL in case of an error.
> + */
> +struct device_node *of_create_node(struct device_node *parent,
> +                                  const char *full_name,
> +                                  struct of_changeset **cset)
> +{
> +       struct of_changeset *ocs;
> +       struct device_node *np;
> +       int ret;
> +
> +       np = __of_node_dup(NULL, full_name);
> +       if (!np)
> +               return NULL;
> +       np->parent = parent;
> +
> +       if (!cset)
> +               return np;
> +
> +       ocs = kmalloc(sizeof(*ocs), GFP_KERNEL);
> +       if (!ocs) {
> +               of_node_put(np);
> +               return NULL;
> +       }
> +
> +       of_changeset_init(ocs);
> +       ret = of_changeset_attach_node(ocs, np);
> +       if (ret) {
> +               of_changeset_destroy(ocs);
> +               of_node_put(np);
> +               kfree(ocs);
> +               return NULL;
> +       }
> +
> +       np->data = ocs;
> +       *cset = ocs;
> +
> +       return np;
> +}
> +EXPORT_SYMBOL(of_create_node);
> +
> +/**
> + * of_destroy_node - Destroy a dynamically created device node
> + *
> + * @np: Pointer to dynamically created device node
> + *
> + */
> +void of_destroy_node(struct device_node *np)
> +{
> +       struct of_changeset *ocs;
> +
> +       if (np->data) {
> +               ocs = (struct of_changeset *)np->data;
> +               of_changeset_destroy(ocs);
> +       }
> +       of_node_put(np);

A sequence like this would be broken:

np  = of_create_node()
of_node_get(np)
of_destroy_node(np)

The put here won't free the node because it still has a ref, but we
just freed the changeset. For this to work correctly, we would need
the release function to handle np->data instead. However, all users of
data aren't a changeset.

I'm failing to remember why we're storing the changeset in 'data', but
there doesn't seem to be a reason now so I think that can just be
dropped. Then if you want to free the node, you'd just do an
of_node_put(). (And maybe after the node is attached you do a put too,
because the attach does a get. Not completely sure.)

A unittest for all these functions would be helpful.

Rob