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SubjectRe: [PATCH/RFC] kbuild: Create a rule for building device tree overlay objects
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Hi Frank,

> On May 16, 2015, at 05:16 , Frank Rowand <frowand.list@gmail.com> wrote:
>
> On 5/15/2015 5:47 PM, Frank Rowand wrote:
>> On 5/12/2015 7:33 AM, Pantelis Antoniou wrote:
>>> Hi Geert,
>>>
>>>> On May 12, 2015, at 14:56 , Geert Uytterhoeven <geert+renesas@glider.be> wrote:
>>>>
>>>> This allows to handle device tree overlays like plain device trees.
>>>>
>>>> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
>>>> ---
>>>> Questions:
>>>> - Do we want dtso files under arch/<arch>/boot/dts/, too?
>>>> - Do we want to move the dts files outside the kernel repository
>>>> first?
>>>>
>>>
>>> Oh that’s a nice hornet’s nest you’ve kicked here.
>>>
>>> arch/<arch>/boot/dts should not be the place, cause overlays are not related with boot per se.
>>> As they are right now are board (family) specific.
>>
>> Aren't overlays meant to describe child boards (capes, shields, whatever) that may
>> vary from system to system, but are not expected to be hot-plugged while the OS
>> is up? Or is hot-plug a design goal?
>
> To reply to myself, there is a current discussion about whether to use overlays to
> help with a powerpc pci desire to add and delete subtrees:
>
> http://www.spinics.net/lists/linux-pci/msg40740.html
>
> That sound like hot-plug to me…
>

Many people asked for overlays with hot-plugging probably busses like PCI and USB.

Think about an FPGA on a PCI board that needs to be instantiated after insertion.

Expect more activity on that particular front; probably this week.

>>
>> If no hot-plug, then to me an overlay is just as related to boot as the base dts.
>> It is a mere implementation detail that overlays are "loaded" from userspace
>> instead of by the booting kernel (I don't really know the details of using
>> overlays, so please correct me if I am wrong about how the kernel becomes aware
>> of an overlay).
>>
>>>
>>> I think we should try to keep an external kernel repo with them for now until we
>>> figure out where to put them.
>>>
>>>> scripts/Makefile.lib | 3 +++
>>>> 1 file changed, 3 insertions(+)
>>>>
>>>> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
>>>> index 79e86613712f2230..4b14eef1d4b2ce8f 100644
>>>> --- a/scripts/Makefile.lib
>>>> +++ b/scripts/Makefile.lib
>>>> @@ -292,6 +292,9 @@ cmd_dtc = mkdir -p $(dir ${dtc-tmp}) ; \
>>>> $(obj)/%.dtb: $(src)/%.dts FORCE
>>>> $(call if_changed_dep,dtc)
>>>>
>>>> +$(obj)/%.dtbo: $(src)/%.dtso FORCE
>>>> + $(call if_changed_dep,dtc)
>>>> +
>>>> dtc-tmp = $(subst $(comma),_,$(dot-target).dts.tmp)
>>>>
>>>> # Bzip2
>>>> --
>>>> 1.9.1
>>>
>>> Regards
>>>
>>> — Pantelis

Regards

— Pantelis



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