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

From: Sudeep Holla
Date: Fri Oct 06 2017 - 09:52:07 EST

On 06/10/17 14:47, Jassi Brar wrote:
> 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".

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.