Re: [PATCH v2 3/7] of: resolver: Add export_symbols in of_resolve_phandles() parameters

[Herve Codina <herve.codina@bootlin.com>]

Hi Luca,

On Fri, 2 May 2025 16:35:59 +0200
Luca Ceresoli <luca.ceresoli@bootlin.com> wrote:

> Hello Hervé,
> 
> On Wed, 30 Apr 2025 14:51:47 +0200
> Herve Codina <herve.codina@bootlin.com> wrote:
> 
> > In order to prepare the introduction of the export symbols node
> > handling, add a export_symbols parameter in of_resolve_phandles().
> > 
> > The export_symbols is the export symbols device tree node the resolver
> > will use for the overlay symbols resolution.
> > 
> > Signed-off-by: Herve Codina <herve.codina@bootlin.com>
> > Tested-by: Ayush Singh <ayush@beagleboard.org>  
> 
> [...]
> 
> > --- a/drivers/of/resolver.c
> > +++ b/drivers/of/resolver.c
> > @@ -237,7 +237,8 @@ static int get_phandle_from_symbols_node(const struct device_node *tree_symbols,
> >  /**
> >   * of_resolve_phandles - Relocate and resolve overlay against live tree
> >   *
> > - * @overlay:	Pointer to devicetree overlay to relocate and resolve
> > + * @overlay:		Pointer to devicetree overlay to relocate and resolve
> > + * @export_symbols:	Pointer to devicetree export symbols node.
> >   *
> >   * Modify (relocate) values of local phandles in @overlay to a range that
> >   * does not conflict with the live expanded devicetree.  Update references
> > @@ -257,6 +258,10 @@ static int get_phandle_from_symbols_node(const struct device_node *tree_symbols,
> >   * corresponding to that symbol in the live tree.  Update the references in
> >   * the overlay with the phandle values in the live tree.
> >   *
> > + * @export_symbols can be use in this references update. The resolver tries
> > + * first to find a match in the @export_symbols. If not found, it uses the
> > + * "__symbol__" node in the live tree.  
> 
> The rationale behind this logic is not clear to me. I'd have expected
> instead this logic:
> 
>   if (export-symbols != NULL):
>       match only in export-symbols
>   else
>       match only in __symbols__
> 
> following the idea that it's better to be strict when introducing
> something, and possibly relax it later on.
> 
> As I see it, with the current logic if you use export-symbols but you
> build dtbs with -@, you can still match a global label. export-symbols
> should avoid that instead.
> 
> Let me know whether I'm missing something here (which is surely
> possible).

No, you don't miss anything, it was just a choice and I have chosen to be
not exclusive between export-symbols and __symbols__.

export-symbols is taken in priority and if the symbol is not found in
export-symbols, we try with __symbols__.

Maybe I should be stricter. I don't have any strong opinion about that.

Ayush, on fdtoverlay what is the choice done ?

If an export-symbols is present and a symbol needs to be resolved but this
symbol is not found in export-symbols, do you try to fing it in __symbols__
or do you simply abort the resolution with an error ?

Best regards,
Hervé