Date:   Thu, 23 Mar 2023 19:11:57 -0700
From:   Lizhi Hou <lizhi.hou@....com>
To:     Rob Herring <robh@...nel.org>
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 3/23/23 15:40, Rob Herring wrote:
> 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.
Got it.
>
>> Signed-off-by: Sonal Santan <sonal.santan@....com>
>> Signed-off-by: Max Zhen <max.zhen@....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: Brian Xu <brian.xu@....com>
>> Signed-off-by: Clément Léger <clement.leger@...tlin.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.
>
>> ---
>>   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

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