From mboxrd@z Thu Jan  1 00:00:00 1970
From: Frank Rowand <frowand.list@gmail.com>
Date: Wed, 29 Jun 2016 19:34:54 -0700
Subject: [U-Boot] [PATCH v3 10/12] libfdt: Add overlay application
	function
In-Reply-To: <20160628031252.GZ4242@voom.fritz.box>
References: <20160624142757.32735-1-maxime.ripard@free-electrons.com>
 <20160624142757.32735-11-maxime.ripard@free-electrons.com>
 <20160627052607.GK4242@voom.fritz.box> <20160627114000.GV4000@lukather>
 <20160628031252.GZ4242@voom.fritz.box>
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On 06/27/16 20:12, David Gibson wrote:
> On Mon, Jun 27, 2016 at 01:40:00PM +0200, Maxime Ripard wrote:
>> Hi David,
>>
>> On Mon, Jun 27, 2016 at 03:26:07PM +1000, David Gibson wrote:
>>>> +static uint32_t overlay_get_target_phandle(const void *fdto, int fragment)
>>>> +{
>>>> +	const uint32_t *val;
>>>> +	int len;
>>>> +
>>>> +	val = fdt_getprop(fdto, fragment, "target", &len);
>>>> +	if (!val || (*val == 0xffffffff) || (len != sizeof(*val)))
>>>> +		return 0;
>>>
>>> This doesn't distinguish between a missing property (which may
>>> indicate a valid overlay using a target-path or some other method)
>>> and a badly formatted 'target' property, which is definitely an error
>>> in the overlay.
>>>
>>> I think those should be treated differently.
>>
>> AFAIK, phandles can have any 32 bits values but 0xffffffff. In order
>> to cover the two cases, we would need to have some error code, but
>> that doesn't really work with returning a uint32_t.
> 
> Actually phandles can have any value except 0xffffffff *or* 0.  So you
> can use 0 for "couldn't find" and -1 for "badly formatted".

< snip >

Hi David,

I would like to capture this for the specification.

It seems like I could say that a value of 0 in the FDT is not allowed.

Then thinking of what Pantelis is doing with overlays, it seems like a
value of 0xffffffff is allowed in the FDT, but it means not a valid
phandle, so do not try to de-reference it.

Does that sound good?

-Frank