On 07/13/17 13:07, Frank Rowand wrote:
> On 07/13/17 12:38, Phil Elwell wrote:
>
> (I moved Phil's reply to after the email he replied to.)
>
>> On 13 Jul 2017 8:32 pm, "Frank Rowand" <frowand.list@xxxxxxxxx> wrote:
>>
>>> On 07/03/17 02:06, David Gibson wrote:
>>>> On Wed, Jun 14, 2017 at 05:52:25PM +0300, Pantelis Antoniou wrote:
>>>>> This patch enables an overlay to refer to a previous overlay's
>>>>> labels by performing a merge of symbol information at application
>>>>> time.
>>>>
>>>> This seems to be doing things the hard way.
>>>>
>>>> You're essentially extending the semantics of overlay application to
>>>> add the symbol merging. You've implemented these extended semantics
>>>> in libfdt, which is all very well, but that's not the only overlay
>>>> application implementation.
>>>>
>>>>
>>>> It seems to me a better approach would be to change dtc's -@
>>>> implementation, so that in /plugin/ mode instead of making a global
>>>> __symbols__ node, it puts it into the individual fragments. That way
>>>> the existing overlay application semantics will update the __symbols__
>>>> node.
>>>
>>> If the __symbols__ node was inside a fragment, then the existing
>>> code would add (or update) a __symbols__ node located at the location
>>> pointed to by the fragment's target path, instead of updating the
>>> node /__symbols__.
>>>
>>> It makes sense to me to have only one global __symbols__ node instead
>>> of several.
>>>
>>> If there is a global __symbols__ node then we have a single name
>>> space for symbols.
>>>
>>> If there are multiple __symbols__ nodes spread throughout the tree,
>>> then to me that would imply different name spaces spread throughout
>>> the tree, where namespaces are determined by fragments. This sounds
>>> confusing to me. Or if the intent is to have a single name space
>>> then the __symbols__ information would be scattered throughout the
>>> tree instead of located in a single node.
>>>
>>> My current patch (under review), targeted for Linux 4.13-rc1, puts
>>> an overlay's __symbols__ node properties into the overlay's
>>> changeset, so they get added when the overlay is loaded and
>>> removed when the overlay is unloaded.
>
>> Can we also consider a mechanism for overlay-local symbols, i.e. symbols
>> that are used purely to create links within an overlay - perhaps using a
>> particular naming convention? This would make it easier to instantiate an
>> overlay multiple times without having to uniquify all symbols, and it would
>> avoid polluting the global namespace without reason.
>>
>> Phil
>
> That is essentially the result you get if you compile the overlay dts
> without '-@'. There will be no __sympls__ node created even if there
^^^^^^^^^^^ __symbols__
> are symbols within the overlay.
>
> This is important if the overlay is for an add-on board which might
> have several instances plugged into different sockets on the base
> system.
>
> But Phil does bring up an interesting use case. If the add-on board
> ("level one add-on") in turn has a socket that an additional board
> ("level two add-on") can be plugged into, then the level two add-on
> overlay might have a need to reference a symbol from the overlay
> for the level one add-on. And since there may be multiple level one
> add-on cards in the system, the overlay for each of the level one
> add-ons would need to export its symbols in a name space only
> visible to the level two add-on plugged into that specific level
> on add-on.
>
> -Frank
>
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