Re: [PATCH v5 6/8] Documentation: bindings: add compatible specific to legacy SCPI protocol

[Sudeep Holla <sudeep.holla@arm.com>]

On 10/11/16 19:03, Olof Johansson wrote:
> On Thu, Nov 10, 2016 at 6:34 AM, Sudeep Holla <sudeep.holla@arm.com> wrote:
>>
>>
>> On 10/11/16 14:12, Rob Herring wrote:
>>>
>>> On Thu, Nov 10, 2016 at 4:26 AM, Sudeep Holla <sudeep.holla@arm.com>
>>> wrote:
>>>>
>>>>
>>>>
>>>> On 10/11/16 01:22, Rob Herring wrote:
>>>>>
>>>>>
>>>>> On Wed, Nov 02, 2016 at 10:52:09PM -0600, Sudeep Holla wrote:
>>>>>>
>>>>>>
>>>>>> This patch adds specific compatible to support legacy SCPI protocol.
>>>>>>
>>>>>> Cc: Rob Herring <robh+dt@kernel.org>
>>>>>> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
>>>>>> ---
>>>>>>  Documentation/devicetree/bindings/arm/arm,scpi.txt | 4 +++-
>>>>>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/Documentation/devicetree/bindings/arm/arm,scpi.txt
>>>>>> b/Documentation/devicetree/bindings/arm/arm,scpi.txt
>>>>>> index d1882c4540d0..ebd03fc93135 100644
>>>>>> --- a/Documentation/devicetree/bindings/arm/arm,scpi.txt
>>>>>> +++ b/Documentation/devicetree/bindings/arm/arm,scpi.txt
>>>>>> @@ -7,7 +7,9 @@ by Linux to initiate various system control and power
>>>>>> operations.
>>>>>>
>>>>>>  Required properties:
>>>>>>
>>>>>> -- compatible : should be "arm,scpi"
>>>>>> +- compatible : should be
>>>>>> +       * "arm,scpi" : For implementations complying to SCPI v1.0 or
>>>>>> above
>>>>>> +       * "arm,legacy-scpi" : For implementations complying pre SCPI
>>>>>> v1.0
>>>>>
>>>>>
>>>>>
>>>>> I'd prefer that we explicitly enumerate the old versions. Are there
>>>>> many?
>>>>>
>>>>
>>>> I understand your concern, but this legacy SCPI protocol was not
>>>> officially released. It was just WIP which vendors picked up from very
>>>> early releases. Since they are not numbered, it's hard to have specific
>>>> compatibles with different versions until v1.0. That's one of the reason
>>>> to retain platform specific compatible so that we can add any quirks
>>>> based on them if needed.
>>>>
>>>> I will probably add these information in the commit log so that it's
>>>> clear why we can't do version based compatible.
>>>
>>>
>>> This is exactly my point. By enumerate, I meant having platform
>>> specific compatibles. Having "arm,legacy-scpi" is pointless because
>>> who knows what version they followed and they may all be different.
>>>
>>
>> OK, but IIUC Olof's concern wanted a generic one along with the platform
>> specific compatible which kind of makes sense as so far we have seen
>> some commonality between Amlogic and Rockchip.
>>
>> E.g. Amlogic follows most of the legacy protocol though it deviates in
>> couple of things which we can handle with platform specific compatible
>> (in the following patch in the series). When another user(Rockchip ?)
>> make use of this legacy protocol, we can start using those platform
>> specific compatible for deviations only.
>>
>> Is that not acceptable ?
>
> If there's no shared legacy feature set, then it's probably less
> useful to have a shared less precise compatible value.
>

There is and will be some shared feature set for sure. At the least the
standard command set will be shared.

> What the main point I was trying to get across was that we shouldn't
> expand the generic binding with per-vendor compatible fields, instead
> we should have those as extensions on the side.
>

Yes I get the point. We will have per-vendor compatibles for handle the
deviations but generic one to handle the shared set.

> I'm also a little apprehensive of using "legacy", it goes in the same
> bucket as "misc". At some point 1.0 will be legacy too, etc.
>

True and I agree, how about "arm,scpi-pre-1.0" instead ?

--
Regards,
Sudeep