linux-kernel - Re: [PATCH v2 2/6] Documentation: devicetree: add bindings to support ARM MHU doorbells

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Date:   Thu, 6 Jul 2017 20:07:54 +0530
From:   Jassi Brar <jassisinghbrar@...il.com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Rob Herring <robh@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Devicetree List <devicetree@...r.kernel.org>,
        Alexey Klimov <alexey.klimov@....com>,
        Jassi Brar <jaswinder.singh@...aro.org>
Subject: Re: [PATCH v2 2/6] Documentation: devicetree: add bindings to support
 ARM MHU doorbells

On Thu, Jul 6, 2017 at 3:03 PM, Sudeep Holla <sudeep.holla@....com> wrote:
>
>
> On 06/07/17 10:27, Jassi Brar wrote:
>> On Thu, Jul 6, 2017 at 2:48 PM, Sudeep Holla <sudeep.holla@....com> wrote:
>>> Hi Jassi,
>>>
>>> On 06/07/17 07:28, Jassi Brar wrote:
>>>> On Wed, Jul 5, 2017 at 11:32 PM, Sudeep Holla <sudeep.holla@....com> wrote:
>>>>
>>>>>
>>>>> I have posted the SCMI patches now[1],
>>>>>
>>>> I wish I was CC'ed on that. Now LKML seems too busy to forward it.
>>>>
>>>
>>> Yes, my mistake, I should have cc-ed you.
>>>
>>>>> please let me know how to get
>>>>> both SCPI and SCMI working together with different doorbell bits on the
>>>>> same channel.
>>>>>
>>>> You say in the cover letter :
>>>> "Let me begin admitting that we are introducing yet another protocol to
>>>> achieve same things as many existing protocols like ARM SCPI, TI SCI,
>>>> QCOM RPM, Nvidia Tegra BPMP, and so on"
>>>>
>>>>  So SCMI is supposed to replace SCPI, SCI, RPM and BPMP   or   SCMI is
>>>> to be used for future platforms.
>>>> If SCPI and SCMI achieve the same, why have them both active simultaneously?
>>>>
>>>
>>> Yes it may not be used, but the firmware might support both for backward
>>> compatibility. E.g. on Juno, we still may continue supporting SCPI while
>>> we transition to SCMI. So both old and new DTs must work.
>>>
>> Sure, but still there is no reason to have both SCMI and SCPI active
>> during _runtime_.
>> Either SCMI or SCPI should be populated by DT, not both.
>>
>>>> Assuming there really is some sane excuse :-
>>>
>>> Yes as I mentioned above.
>>>
>> If you specify only one of SCPI/SCMI, you wouldn't need the shim arbitrator.
>>
>
> I said it *may not be used*, currently it is used.
>
SCPI provides more than what SCMI currently does - dvfs, clock, sensor.
I see no reason why you must have SCPI and SCMI both running.

And even then there is a solution - a shim arbitrator. Other
platforms, those share a channel, do that. No big deal.

 BTW, I hope you realise that we need a 'transport layer' which will
be the platform specific glue between mailbox controller specifics and
the generic SCMI code.
I see your confusion in the form of some issues in the SCMI
implementation, please CC me on the next revision.

Thanks.