Re: [PATCH v4 2/8] OF: Introduce DT overlay support.

[Pantelis Antoniou]

Hi Sebastian,

On May 26, 2014, at 6:09 PM, Sebastian Reichel wrote:

> Hi,
> 
> On Mon, May 26, 2014 at 02:55:37PM +0300, Pantelis Antoniou wrote:
>> On May 26, 2014, at 2:23 PM, Grant Likely wrote:
>>> On Mon, 26 May 2014 12:57:32 +0200, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
>>> Heeheehee. We're back where we started. The original question is whether
>>> or not that is a valid approach. If the overlay represents something
>>> that can be hot plugged/unplugged, then passing it through to the second
>>> kernel would be the wrong thing to do. If it was a permenant addition,
>>> then it probably doesn't need to be removed.
>>> 
>>> We do actually keep the overlay info in memory for the purpose of
>>> removal exactly so we can support hot unbinding of devices and drivers
>>> that make use of overlays.
>> 
>> We can support either method. I am not feeling any wiser about which one should be
>> the default TBH, so what about exporting a property and let the platform 
>> figure out which is more appropriate?
> 
> What about supporting "negative" overlays (so an overlay, that
> removes DT entries)? That way one could reverse apply an overlay.
> All the dependency stuff would basically be the users problem.  The
> kernel only checks if it can apply an overlay (and return some error
> code if it can't). This this code is needed anyway to check the
> input from userspace.
> 
> As a result the overlay handling would basically have the same
> behaviour as diff and patch :)
> 

This is already supported; nodes and properties can be prefixed with a minus
sign '-' and operate as expected :)

i.e. "-property;" removes a property and "-node { };" removes a node. 

> P.S.: Sorry if this has already been suggested. I have only read
> mails from PATCHv4.
> 
> -- Sebastian

Regards

-- Pantelis

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