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 14:57:42 +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 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.