linux-kernel - Re: [PATCH] mailbox: add support for doorbell/signal mode controllers

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Date:   Wed, 1 Nov 2017 23:33:34 +0530
From:   Jassi Brar <jassisinghbrar@...il.com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Arnd Bergmann <arnd@...db.de>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Subject: Re: [PATCH] mailbox: add support for doorbell/signal mode controllers

On Wed, Nov 1, 2017 at 10:02 PM, Sudeep Holla <sudeep.holla@....com> wrote:

>
> Such controllers don't need to transmit any data, they just transmit
> the signal. In such controllers the data pointer passed to
> mbox_send_message is passed to client via it's tx_prepare callback.
> Controller doesn't need any data to be passed from the client.
>
Some controllers need a non-zero value written to a register in order
to trigger the signal.
That register is visible to the remote. While the data/packet is setup
during tx_prepare() callback.
You are overlooking this class of doorbell controllers.

>
> This is rough idea I have on extending mailbox interface to support
> the doorbell requirements.
>
What doorbell requirements does the api not support?
QComm's APCS IPC is what you call a "doorbell" controller and is
already supported by the API. It could run SCMI even easier than MHU
(your controller).

> The new API send_signal will eliminate the
> issue Jassi has explained in earlier discussion with respect to generic
> message format using Rockchip example.
>
Sorry I don't see how.
Please explain how can send_signal() api be used by, say, rockchip to
support SCMI?

I am not convinced we should clone an api just so that a client driver
becomes simpler. Esp when it shifts, and not avoid, the additional
code (to support the client) onto the provider side.

Thanks.