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

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Date:	Tue, 24 Jun 2014 10:12:52 +0200
From:	Alexander Sverdlin <alexander.sverdlin@....com>
To:	ext Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
	Ioan Nicu <ioan.nicu.ext@....com>
CC:	Grant Likely <grant.likely@...retlab.ca>,
	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!

On 23/06/14 21:13, ext Pantelis Antoniou wrote:

[...]

>>> 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) !=
>> 				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.
>>
> 
> If that's the case, the code in irq.c is wrong.
> 
> interrupt-controller is a bool property; the correct call to use is of_property_read_bool()
> which returns true or false when the value is defined.

No, it's not bool... It's an existence of a void property. 

> The use of of_get_property is a bug here. It is perfectly valid for a property to have a
> NULL value when length = 0.

of_find_property() would be really correct in this particular case...

-- 
Best regards,
Alexander Sverdlin.
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