linux-kernel - Re: [PATCH v3 16/22] firmware: arm_scmi: add arm

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Message-ID: <25023d1a-a221-b131-5a1e-7d909b006d1b@arm.com>
Date:   Fri, 6 Oct 2017 14:51:57 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Jassi Brar <jassisinghbrar@...il.com>
Cc:     Sudeep Holla <sudeep.holla@....com>, Arnd Bergmann <arnd@...db.de>,
        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>, Loc Ho <lho@....com>,
        Alexey Klimov <alexey.klimov@....com>,
        Ryan Harkin <Ryan.Harkin@....com>
Subject: Re: [PATCH v3 16/22] firmware: arm_scmi: add arm_mhu specific mailbox
 interface



On 06/10/17 14:47, Jassi Brar wrote:
> On Fri, Oct 6, 2017 at 7:02 PM, Sudeep Holla <sudeep.holla@....com> wrote:
>>
>>
>> On 06/10/17 12:26, Jassi Brar wrote:
>>> On Wed, Oct 4, 2017 at 5:06 PM, Arnd Bergmann <arnd@...db.de> wrote:
>>>> On Thu, Sep 28, 2017 at 3:11 PM, Sudeep Holla <sudeep.holla@....com> wrote:
>>>>> This patch adds ARM MHU specific mailbox interface for SCMI.
>>>>>
>>>>> Cc: Arnd Bergmann <arnd@...db.de>
>>>>> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
>>>>
>>>> This clearly needs an explanation why we need another driver.
>>>>
>>> Yes the patch needs explanation which is that we need a shim layer to
>>> map SCMI requests onto what the underlying controller expects. The
>>> alternative was to clone the controller driver (MHU now and others
>>> later when their platforms support SCMI) and pretend SCMI is the only
>>> client they are ever going to serve.
>>>
>>
>> Again that's not the point, doorbell is more common feature and that can
>> be supported. As SCMI expects doorbell feature in the specification, it
>> just need to support that class of controllers.
>>
> NO.  All SCMI expects is SHMEM and a signal reaching the other end.
> The signal mechanism need not necessarily be "doorbell".
> 

Agreed, but creating an abstraction ro do something as generic as
doorbell and writing shim layer for each controller to use SCMI also
sounds bad.

-- 
Regards,
Sudeep