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

[Guenter Roeck <linux-0h96xk9xTtrk1uMJSBkQmQ@public.gmane.org>]

On 05/26/2014 08:09 AM, 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-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org> 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.
>

Does that mean that I would need to describe such a negative overlay
for each overlay to be able to get it removed ?

This would introduce an endless source of problems with bad "reverse"
overlay descriptions. Sure, that would "be the users problem",
but I don't think that would make it better.

Guenter

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