linux-kernel - Re: [PATCH 5/6] OF: Utility helper functions for dynamic nodes

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Date:	Tue, 24 Jun 2014 10:10:01 +0200
From:	Alexander Sverdlin <alexander.sverdlin@....com>
To:	Ioan Nicu <ioan.nicu.ext@....com>,
	ext Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
	Grant Likely <grant.likely@...retlab.ca>
CC:	Rob Herring <robherring2@...il.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Matt Porter <matt.porter@...aro.org>,
	Koen Kooi <koen@...inion.thruhere.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alison Chaiken <Alison_Chaiken@...tor.com>,
	Dinh Nguyen <dinh.linux@...il.com>,
	Jan Lubbe <jluebbe@...net.de>, Michael Stickel <ms@...able.de>,
	Guenter Roeck <linux@...ck-us.net>,
	Dirk Behme <dirk.behme@...il.com>,
	Alan Tull <delicious.quinoa@...il.com>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Michael Bohan <mbohan@...eaurora.org>,
	Michal Simek <monstr@...str.eu>,
	Matt Ranostay <mranostay@...il.com>,
	Joel Becker <jlbec@...lplan.org>, devicetree@...r.kernel.org,
	Wolfram Sang <wsa@...-dreams.de>, linux-i2c@...r.kernel.org,
	Mark Brown <broonie@...nel.org>, linux-spi@...r.kernel.org,
	linux-kernel@...r.kernel.org, Pete Popov <pete.popov@...sulko.com>,
	Dan Malek <dan.malek@...sulko.com>,
	Georgi Vlaev <georgi.vlaev@...sulko.com>
Subject: Re: [PATCH 5/6] OF: Utility helper functions for dynamic nodes

Hi Pantelis, Grant,

On 23/06/14 20:33, Ioan Nicu wrote:
>>> On 22/06/14 11:40, ext Pantelis Antoniou wrote:
>>>> Introduce helper functions for working with the live DT tree,
>>>> all of them related to dynamically adding/removing nodes and
>>>> properties.
>>>>
>>>> __of_copy_property() copies a property dynamically
>>>> __of_create_empty_node() creates an empty node
>>>>
>>>> Bug fix about prop->len == 0 by Ionut Nicu <ioan.nicu.ext@....com>
>>>
>>> Are you sure about this? (see below...)
>>>
> 
> Alexander is right, my fix was lost even though it's mentioned in this patch.
> 
>>>> Signed-off-by: Pantelis Antoniou <pantelis.antoniou@...sulko.com>
>>>> ---
>>
>> [snip]
>>>> +
>>>> +	if (prop->length > 0) {
>>>        ^^^^^^^^^^^^^^^^^^^^^
>>> Seems, that length==0 case will still produce value==NULL results,
>>> which will brake some checks in the kernel... Or am I missing something in
>>> the new version?
>>>
>>
>> prop->value will be set to NULL, and length will be set to zero (kzalloc).
>> This is a normal zero length property.
>>
>> I don't know of any place in the kernel accessing the value if prop->length==0
>>
> 
> We have a simple use case. We have an overlay which adds an interrupt controller.
> If you look in drivers/of/irq.c, in of_irq_parse_raw():
> 
> [...]
> 	/* Now start the actual "proper" walk of the interrupt tree */
> 	while (ipar != NULL) {
> 		/* Now check if cursor is an interrupt-controller and if it is
> 		 * then we are done
> 		 */
> 		if (of_get_property(ipar, "interrupt-controller", NULL) !=

We have to define, if it's allowed for an empty property to have NULL value.
Several places in the kernel use of_get_property() to check for property existence.
We either have to make a tree-wide patch and replace of_get_property() with of_find_property() in those cases,
or ensure value != NULL in this copy function...

Grant, what do you think?

> 				NULL) {
> 			pr_debug(" -> got it !\n");
> 			return 0;
> 		}
> [...]
> 
> A node is identified as an interrupt controller if it has a zero-length property
> called "interrupt-controller" but with a non-NULL value.
> 
> My proposed fix for this was to remove the if () condition. propn->value will be
> allocated with kmalloc(0) which returns ZERO_SIZE_PTR which is != NULL.
> 
> 
>>
>> [snip]
>>
>>>> +
>>>> #endif /* _LINUX_OF_H */
>>>>
>>>
>>> -- 
>>> Best regards,
>>> Alexander Sverdlin.
>>
>> Regards
>>
>> -- Pantelis
>>
> 
> Regards,
> Ionut Nicu
> 

-- 
Best regards,
Alexander Sverdlin.
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