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

[Lizhi Hou]

On 3/23/23 15:40, Rob Herring wrote:
> On Thu, Jan 19, 2023 at 9:02 PM Lizhi Hou <lizhi.hou@xxxxxxx> 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@xxxxxxx>
> Your Sob should be last because you sent this patch. The order of Sob
> is roughly the order of possession of the patch.
Got it.
> > Signed-off-by: Sonal Santan <sonal.santan@xxxxxxx>
> > Signed-off-by: Max Zhen <max.zhen@xxxxxxx>
> So Sonal and Max modified this patch?
They did not directly modify the code. And we discussed the design 
together.  They also reviewed the patch before I sent it out. Please let 
me know if other keyword should be used in this case.
> > Reviewed-by: Brian Xu <brian.xu@xxxxxxx>
> > Signed-off-by: Clément Léger <clement.leger@xxxxxxxxxxx>
> Why does this have Clément's Sob?
I referenced Clément 's code and used one portion in my first patch 
series. And I re-implemented it later to address the code review 
comments/requests.
> > ---
> >   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().
Sure.
> > + *
> > + * @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.)

The question is how to save changeset and free it later. I used global 
link list to track the changeset been created.

Storing the changeset in 'data' can avoid using the global link list.

To use of_node_put() to free both node and changeset, I think we can

  1) add a new flag, then in of_node_release() we can know np->data is 
changeset by checking the flag.

  2) When creating node, allocate extra memory for changeset and set 
np->data to a global function of_free_dynamic_node().

      In of_node_release(), check if np->data == of_free_dynamic_node, 
call of_free_dynamic_node(np).

      in of_free_dynamic_node(), free changeset by 
of_changeset_destroy(np+1)

Does this make sense to you? If yes, 1) or 2) sounds better?

> A unittest for all these functions would be helpful.

Ok, I will create unittest for the new added functions.


Thanks,

Lizhi

> Rob