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

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Message-ID: <f142dac2-a27c-4c46-4d22-4df4f2e8cfb1@arm.com>
Date:   Fri, 6 Oct 2017 14:32:00 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Jassi Brar <jassisinghbrar@...il.com>,
        Arnd Bergmann <arnd@...db.de>
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>, 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 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.

> BTW, I haven't reviewed this patchset yet so I am not sure about this
> code but I do believe we need a transport layer (this shim driver)
> between generic SCMI implementation and each controller driver.
> 

Again Arnd's point was to extend mailbox API instead of adding this
abstract layer which I think is more elegant. The controllers that
can provide that feature will support that.

-- 
Regards,
Sudeep