Unifying cape overlays into boot .dtb for BeagleBoard.org boards

[Pantelis Antoniou]

Hi Russell,

On Jun 17, 2014, at 8:05 PM, Russell King - ARM Linux wrote:

> On Tue, Jun 17, 2014 at 07:59:21PM +0300, Pantelis Antoniou wrote:
>> That case might already work on FPGA people's trees. I know Altera for sure
>> uses overlays, and some xilinx guys popped up on past discussions.
>> Their vendor trees probably use an older revision of the patches.
>> 
>> BTW, there is nothing special about DRM/v4l2 that can't be handled by
>> a generic DT mechanism. What makes this such a big problem?
> 
> Really?
> 
> DRM is not hotpluggable in any shape or form, and David Airlie has
> indicated that he does strongly opposes moving it in that direction.
> 
> DRM follows the "card" model, where, at probe time, the hardware is
> known and never changes until the "card" is torn down.  No new
> connectors can be added once the "card" is initialised, and no
> connectors can be removed.  Any changes must be done by tearing down
> the entire card and reconstructing it (if reconstructing it with a
> reduced set of hardware is appropriate.)
> 

That is a limitation of the current DRM implementation.

I seems to be this is born out of some kind of misunderstanding about how
DT can (and does) support dynamic changes.

I admit that I haven't done much work on DRM (besides some tinkering with
Rob Clark's ti_lcdc DRM driver), but knowing what DT does have a dynamic
change notifier support, perhaps it can be made to work.

As I said, the next thing coming is transactional DT support, perhaps you
can share the DT fragment describing your use-case (before/after) and 
I'll try to accommodate in the next patch series.

Regards

-- Pantelis

> -- 
> FTTC broadband for 0.8mile line: now at 9.7Mbps down 460kbps up... slowly
> improving, and getting towards what was expected from it.