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Date:   Thu, 2 Nov 2017 10:51:33 +0000
From:   Sudeep Holla <>
To:     Bjorn Andersson <>
Cc:     Jassi Brar <>,
        Sudeep Holla <>,
        Linux Kernel Mailing List <>,
        Arnd Bergmann <>
Subject: Re: [PATCH] mailbox: add support for doorbell/signal mode controllers

On 01/11/17 22:12, Bjorn Andersson wrote:
> On Wed 01 Nov 11:03 PDT 2017, Jassi Brar wrote:
>> On Wed, Nov 1, 2017 at 10:02 PM, Sudeep Holla <> wrote:
> [..]
>>> 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).
> I agree; from a mbox consumer perspective a doorbell should be a mailbox
> channel that when signalled will ring the bell, i.e. the message is not
> significant and should not be provided by the client.


> If the message is significant and is not derived from the mailbox
> channel (e.g. channel id -> bit in register) it is not a mailbox
> doorbell, it's s regular mailbox used as a doorbell.

Agreed, in my case(ARM MHU) it's indeed a register bit.

> The potential improvement I see in the Qualcomm case is to wrap the
> mbox_send_message(chan, NULL); mbox_client_txdone(chan, 0); calls in one
> simple "mbox_ring_door_bell(chan)" - but I haven't investigated the
> validity of this as a generic function.

Yes that's exactly what I want to do as we make progress with this
patch. For that we find need to add send_signal(chan), instead of
send_data(chan, data).

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