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 10:33:27 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Jassi Brar <jassisinghbrar@...il.com>
Cc:     Sudeep Holla <sudeep.holla@....com>, 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 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. Also can you please
answer other questions I had on mailbox API and not breaking SCPI
exiting users ? I need your suggestion to proceed on that. Similar to
SCPI, SCMI will be used by other platforms which must have doorbell
mailbox mechanism.

-- 
Regards,
Sudeep