Re: [PATCH v3 16/22] firmware: arm_scmi: add arm_mhu specific mailbox interface

[Jassi Brar]

On Fri, Oct 6, 2017 at 7:02 PM, Sudeep Holla <sudeep.holla@xxxxxxx> wrote:
>
>
> On 06/10/17 12:26, Jassi Brar wrote:
>> On Wed, Oct 4, 2017 at 5:06 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote:
>>> On Thu, Sep 28, 2017 at 3:11 PM, Sudeep Holla <sudeep.holla@xxxxxxx> wrote:
>>>> This patch adds ARM MHU specific mailbox interface for SCMI.
>>>>
>>>> Cc: Arnd Bergmann <arnd@xxxxxxxx>
>>>> Signed-off-by: Sudeep Holla <sudeep.holla@xxxxxxx>
>>>
>>> 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".