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

[Rob Herring <robh@kernel.org>]

On Thu, Mar 23, 2023 at 9:12 PM Lizhi Hou <lizhi.hou@amd.com> wrote:
>
>
> On 3/23/23 15:40, Rob Herring wrote:
> > On Thu, Jan 19, 2023 at 9:02 PM Lizhi Hou <lizhi.hou@amd.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@amd.com>
> > 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@amd.com>
> >> Signed-off-by: Max Zhen <max.zhen@amd.com>
> > 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 or nothing. Some feel that only reviews on public lists
should get that tag and internal, private reviews don't matter.

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

Then it goes first or you can use the 'Co-developed-by' tag.

> >
> >> ---
> >>   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?

Neither works. Changesets and nodes are not 1:1 in general though they
are in your use. So you can use the data ptr, but the caller has to
decide that, not the DT core code.

Rob