linux-kernel - Re: [PATCH v3 03/22] dt-bindings: arm: scmi: add ARM MHU specific mailbox client bindings

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Date:   Mon, 9 Oct 2017 15:37:25 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Rob Herring <robh@...nel.org>,
        Jassi Brar <jassisinghbrar@...il.com>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        ALKML <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        Roy Franz <roy.franz@...ium.com>,
        Harb Abdulhamid <harba@...eaurora.org>,
        Nishanth Menon <nm@...com>, Arnd Bergmann <arnd@...db.de>,
        Loc Ho <lho@....com>, Alexey Klimov <alexey.klimov@....com>,
        Ryan Harkin <Ryan.Harkin@....com>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v3 03/22] dt-bindings: arm: scmi: add ARM MHU specific
 mailbox client bindings



On 09/10/17 14:52, Rob Herring wrote:
> On Fri, Oct 6, 2017 at 9:26 PM, Jassi Brar <jassisinghbrar@...il.com> wrote:
>> On Fri, Oct 6, 2017 at 9:24 PM, Rob Herring <robh@...nel.org> wrote:
>>> On Fri, Oct 6, 2017 at 6:01 AM, Jassi Brar <jassisinghbrar@...il.com> wrote:
>>>> On Fri, Oct 6, 2017 at 4:50 AM, Rob Herring <robh@...nel.org> wrote:
>>>>> On Thu, Sep 28, 2017 at 02:11:27PM +0100, Sudeep Holla wrote:
>>
>>>>>
>>>>>> +- mbox-data : For each phandle listed in mboxes property, an unsigned 32-bit
>>>>>> +           data as expected by the mailbox controller
>>>>>
>>>>> Shouldn't that be cells as part of mboxes property?
>>>>>
>>>> A MHU client can send any number of commands (such u32 values) over a channel.
>>>> This client (SCMI) sends just one command over a channel, but other
>>>> clients may/do send two or more.
> 
> The above definition doesn't support 2 or more as it is 1-1 with channels.
> 

In case of MHU, we just need one u32 per channel in SCMI context.

>>> Okay, then I guess I don't understand why this is in DT.
>>>
>> Yeah the client has to provide code (u32 value) for the commands it
>> sends, and that value is going to be platform specific. For example,
>> on Juno the ITS_AN_SCMI_COMMAND may be defined as BIT(7) while on my
>> platform it may be 0x4567
>>
>> For MHU based platforms, it becomes easy if the u32 is passed from DT.
>> And that should be ok since that is like a h/w parameter - a value
>> chosen/expected by the remote firmware.
> 
> Could it ever be more than 1 cell?
> 

No, as mentioned above.

> I guess being in DT is fine, but I'm still not sure about the naming.
> The current name suggests it is part of the mbox binding. Do we want
> that or should it be SCMI specific? Then "data" is vague. Perhaps
> "scmi-commands"?
> 

How about "scmi-mhu-commands" ? As scmi-commands sounds too generic
and part of SCMI specification. But they are rather MHU specific to
make use of each 32 bit in physical channel for a virtual channel.
IOW, it's just different way of representing the doorbell bits I
proposed previously as a 32-bit command expected by the driver.

-- 
Regards,
Sudeep