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Date: Tue, 24 Jun 2014 10:12:52 +0200
From: Alexander Sverdlin <alexander.sverdlin@nsn.com>
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To: ext Pantelis Antoniou <pantelis.antoniou@konsulko.com>,
        Ioan Nicu <ioan.nicu.ext@nsn.com>
CC: Grant Likely <grant.likely@secretlab.ca>,
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        Georgi Vlaev <georgi.vlaev@konsulko.com>
Subject: Re: [PATCH 5/6] OF: Utility helper functions for dynamic nodes
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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.