linux-kernel - Re: [PATCH v3 15/22] firmware: arm_scmi: abstract mailbox interface

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Date:   Wed, 4 Oct 2017 13:24:03 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     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>,
        Jassi Brar <jassisinghbrar@...il.com>
Subject: Re: [PATCH v3 15/22] firmware: arm_scmi: abstract mailbox interface

On Thu, Sep 28, 2017 at 3:11 PM, Sudeep Holla <sudeep.holla@....com> wrote:
> Some of the mailbox controller expects controller specific data in order
> to implement simple doorbell mechanism as expected by SCMI specification.
>
> This patch creates a shim layer to abstract the mailbox interface so
> that it can support any mailbox controller. It also provides default
> implementation which maps to standard mailbox client APIs, so that
> controllers implementing doorbell mechanism need not require any
> additional layer.
>
> Cc: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: Sudeep Holla <sudeep.holla@....com>

Another level? Now we have three levels of stacked mailboxes, with
the highest level being the combined mailbox/memory, then the shim,
and below it the hardware mailbox.

Can you try to come up with a way to do this with fewer abstractions?

Maybe you could assume that the mailbox itself can take variable-length
data packets, and then use the shim here for those that require
something else?

        Arnd