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

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Date:   Fri, 7 Jul 2017 00:07:20 +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 10:14 PM, Sudeep Holla <sudeep.holla@....com> wrote:
>
> On 06/07/17 15:37, Jassi Brar wrote:
>> On Thu, Jul 6, 2017 at 3:03 PM, Sudeep Holla <sudeep.holla@....com> wrote:
>

>> I see no reason why you must have SCPI and SCMI both running.
>>
>
> We can still have 2 different protocols using same MHU channel with
> different doorbells, what's wrong with that ?
>
Only for SCMI and SCPI - both written by same person to achieve the
same thing - I think it should not be necessary.

But yes, SCMI running alongside some complementary protocol (that
implements what SCMI doesn't provide) is a very solid usecase. And
that is the reason you need a platform specific 'transport layer'.

>> And even then there is a solution - a shim arbitrator. Other
>> platforms, those share a channel, do that. No big deal.
>>
>
> Example please? Please remember these protocols are generic and we
> can't add any platform specific code into them.
>
You do need to have platform specific glue as I said.

>>  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.
>
> Why ?
>
Because you should not restrict the usage of SCMI to only platforms
with mailbox controller that does not require any information to
trigger a signal on the other side -- what you call "doorbell".

Why shouldn't Rockchip be able to implement SCMI? Just because it uses
different mechanism to signal the other end?

You are actually putting in effort to restrict the usage of SCMI. Its
like you buy a usb device and the first thing you do is solder it to
the plug.


> Clearly you have not made a since technical argument so far as why
> MHU doorbell is not correct way even when MHU specification is clearly
> allows it. I have given example of ST mailbox which has this doorbell
> kind of support.
>
>> I see your confusion in the form of some issues in the SCMI
>> implementation, please CC me on the next revision.
>>
>
> Care to elaborate on what's my confusion or at-least what you think so ?
>
See me last point.

> Also if you have concern on implementation, ok we can discuss further.
> But can you make it clear as what your objections are for the doorbell
> MHU binding. How will I get the bit assigned for different protocols
> which are platform specific ? I still need some binding , right ?
>
Sorry, No. I'll try to get lkml fwd me the patchset so I can explain
there further.