[U-Boot] [PATCH v3 10/12] libfdt: Add overlay application function

[David Gibson]

On Wed, Jun 29, 2016 at 07:34:54PM -0700, Frank Rowand wrote:
> 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?

That should be ok.  Basically both 0 and -1 are invalid phandle
values, so it's up to us if we want to assign them specific "error"
meanings.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson
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