RFC: proposal to extend the open-pic interrupt specifier definition
Grant Likely
grant.likely at secretlab.ca
Wed Jan 13 17:06:10 EST 2010
On Tue, Jan 12, 2010 at 11:36 AM, Yoder Stuart-B08248
<B08248 at freescale.com> wrote:
>> > The advantage of the above approach is backwards compatibility.
>> > Existing interrupt specifiers (and device trees) are valid with
>> > this proposal.
>>
>> Actually they're not, like BenH pointed out.
>
> The proposal is backwards compatible. An existing interrupt
> specifier (e.g. interrupts = <24 2>;) retains its exact
> same meaning. Old device trees do not need to change
> to comply with the proposal.
You also need to deal with the case of old drivers incorrectly binding
to and trying to understand the new data.
> I'm not directly familiar with the case Ben pointed out, but
> it sounded like Apple used the 1st cell in some non-standard
> way.
>
> It is true that openpic drivers would need to change to handle
> the new specifier-- minimally masking the level/sense field
> to 2 bits.
Which makes the new binding incompatible with old kernels/drivers
which just leads to confusion. It's not worth toying with. Just
create a new compatible value for this new binding and be done with
it. When a driver gets modified to handle the new behaviour, then it
can be also changed to bind against the new compatible value too.
g.
--
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
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